Vol.
167,
March
No.
30.
3, 1990
BIOCHEMICAL
AND
BIOPHYSICAL
RESEARCH
COMMUNICATIONS
Pages
1990
1400-1405
IDENTIFICATIOfJ OF HIGH AND LOW (GTP-SENSITIVE) AFFINITY [ HIGLIBENCLAMIDE BINDING SITES IN CARDIAC VENTRICULAR MEMBRANES J.F.
L.C.
French,
Cardiovascular
Riera
and J.G.
Sarmiento
Bristol-Myers Squibb, PRDD, Pharmacology, Wallingford,
CT 06492
Received February 1, 1990
SUMMARY: Glibenclamide is an antagonist of the ATP-modulated K+ channel in cardiac tissue. This study showed glibenclamide to bind to high (0.2 nM) and low (40 nM) affinity binding sites in canine ventricular membranes. Gpp[NH]p significantly altered the binding characteristics of the low affinity site, while those of the high affinity site were unchanged. This indicates independence of the two sites and suggests the low affinity site may be coupled to a Gbinding protein. Although we have identified two [3H]glibenclamide binding sites, the importance of these sites to the cardiac effects of glibenclamide remains to be determined. 0 1990Academic PESS,Inc.
The ATP-modulated beta
cells
(l-3),
and
cortical
K+ channel
cardiac
neurons
cells
(7).
has been identified (4-S),
The
most
skeletal potent
in pancreatic muscle
inhibitor
cells of
(6) this
channel to date is the sulfonylurea, glibenclamide. Binding sites for [3H]glibenclamide have been identified in insulinoma cells (8), pancreatic in chicken channel ischemia,
beta cells (9), cerebral cortex (8) and more recently and guinea pig heart microsomes (10). Inhibitors of this be potentially useful compounds during cardiac since they are capable of restoring normal or near normal
may
action shown
potential properties (10). Moreover, glibenclamide has been to prevent ischemia-induced ventricular fibrillation in isolated rat hearts (11-12). In the present study, we report the existence of two [3H]glibenclamide binding sites in canine heart ventricular membranes. These sites appear to be distinct since only the binding characteristics of the low affinity site are altered
by guanine
nucleotides. METHODS
Membrane Preparation. Dogs of either sex were anesthetized with pentobarbital (35 mg/kg) and their hearts rapidly removed and placed in ice-cold saline. The ventricles were dissected from the 0006-291X/90$1.50 Copyright All rights
0 1990 by Academic Press, Inc. of reproduction in any form reserved.
1400
Vol.
167,
No.
3, 1990
BIOCHEMICAL
AND
BIOPHYSICAL
RESEARCH
COMMUNICATIONS
atria and weighed. The ventricular tissue was then cut into small pieces and placed in ice-cold buffer solution (250 mM sucrose and 50 mM Tris-HCl, pH 7.4). The tissue was then homogenized four times in a blender at high speed for 20 set each. The homogenate was further homogenized by three treatments with a Brinkman Polytron for 10 set each at a speed setting of seven. The homogenate was then centrifuged at 1100 x g for 10 min. The resulting supernatant fraction was filtered through two layers of cheesecloth and then centrifuged at 12800 x g for 10 min. The supernatant fraction from this treatment was then centrifuged at 105000 x g for 35 min. The resulting pellet was resuspended in a small volume of buffer solution. The membrane preparations were rapidly frozen in liquid nitrogen and stored at -7O'C. Protein determinations were performed with Coomassie Protein Assay Reagent (Pierc Rockford, IL.) using bovine serum albumi as standard. ,f' HlGlibenclamide Bindinq Assavs. The [ Hlglibenclamide binding assays were performed in 50 mM Tris-HCl (pH 7.4) in a final volume of 0.5 ml. Each assay tube contained 250-500 ug of membrane protein and the desired concentration of [3H]glibenclamide (custom labeled by New England Nuclear, specific activity 50 Ci/mmole). The samples were incubated for 90 min at 22'C and then the reaction was terminated by dilution with 5 ml of ice-cold 50 mM Tris-HCl buffer and vacuum filtration on Whatman GF/C filters followed by quick washings of the filters three times with 5 ml of the same buffer. The filters were submerged in 5 ml scintillation fliud and the radioactivity was measured by liquid Scintillation spectroscopy. Specific binding of [3H]glibenclamide was defined as the amount of radioactivity displaced by 50 uM gliquidone, a structurally similar compound. Specific [3H]glibenclamide binding was proportional to protein content up to 1200 ug/ml. K and Bmax values were determined by the EBDA and LIGAND programs A 3,14). obtained from BoehringerMaterials. Gliqiudone was Ingelheim. Glibenclamide, Guanosine 5'-[B,y-imino]triphosphate (Gpp[NH]p) and all other chemical used were obtained from Sigma Chemical Co. (St. Louis, MO.).
Radioligand
RESULTS experiments
binding
the existence of [3H]glibenclamide ventricular membranes. Scatchard of [3H]glibenclamide ['H]glibenclamide constant a binding
(KD) site
binding
for the density
indicated sites
were
performed
high affinity (Bmax ) of 6.4
site was 0.22 + 0.9 fmols/mg
K,, for the second, lower affinity, site was affinity site expected the density of the lower greater (Bmax = 295 + 64 fmols/mg protein). sites, To verify the existence of two inhibition of and gliquidone
[3H]glibenclamide (Figure 2).
binding by these compounds = 0.9 + 0.02 and 10 + 0.3
to
determine
binding sites in canine analysis of the direct binding the existence of two The dissociation (Figure 1).
binding Inhibition was monophasic nM, respectively). 1401
& 0.07 nM with protein. The
40 f 11 nM. was considerably we
studied
As
the
by unlabeled glibenclamide of 0.3 nM [3H]glibenclamide and of high affinity In contrast, at
(Ki 3 nM
Vol.
167,
No.
BIOCHEMICAL
3, 1990
0
AND
BIOPHYSICAL
3
6
RESEARCH
COMMUNICATIONS
9
12
BOUND (fmole) Scatchard plot of ['Hlglibenclamide binding. Fioure 1. The ratio of bound ['Hlglibenclamide to free (B/F) ['Hlglibenclamide was plotted against the concentration of bound ['H]glibenclamide. Canine ventricular membranes were incubated for 90 min with increasing concentrations of ['Hlglibenclamide and binding was determined as described in "Methods." Each value was obtained from triplicate determinations. The experiment presented is representative of 5 experiments.
a biphasic displacement curve [3H]glibenclamide, These results are consistent with the identification sites
by direct Experiments
distinct of the of
A)
binding were
methods described above. carried out to determine
of two binding if
these were The ability
sites or affinity states of the same site. nonhydrolyzable GTP analog, Gpp[NH]p, to alter the binding was explored. ventricular membranes to
B)
100
0
1E :-10
was observed.
lE-9
lE-8
lE-7
4
lE-6
DRUG (M)
100
0
lE-9
I lE-8
lE-7
lE-6
lE-5
DRUG (M)
Figure 2. Inhibition of ]'H]glibenclamide binding by nonlabeled glibenclamide (0) and gliquidone (B) at (A) 0.3 and (B) 3 nM ["Hlglibenclamide. Percent specific binding in the absence of inhibitors is indicated. Each value is expressed as a mean + SEM of three experiments of triplicate determinations.
1402
lE-4
Vol.
167,
No.
3, 1990
BIOCHEMICAL
AND
BIOPHYSICAL
RESEARCH
COMMUNICATIONS
120-
1
Fisure 3. Gpp[NHlp. expressed determinations.
to was
of
significantly
binding by Each value of triplicate
inhibiting
, a concentration
both the high concentration
Gpp[NH]p on the 3 [ Hlglibenclamide performed
lOI30
CONCENTRATION (PM) Inhibition of 3 nM ['Hjglibenclamide Percent specific binding is indicated. as a mean + SEM of three experiments
Gpp[NH]p was capable 3 nM L3H]glibenclamide binds effect
100
lb
of
labeled
binding ligand
and low affinity sites (Figure dependent. To determine the
individual
binding
sites,
characteristics
saturation
in the presence
binding
of Gpp[NH]p.
of the high affinity site those of the lower affinity Bmax of the lower affinity
binding
site
appear
Table Site
be
affinity
to those
2 B max
Control
0.22+0.07
6.450.9
40.1f11.4
295t64
+GPP[NHIP
0.14+0.05
l3.0+1.2
5.7k1.6
20.5+2.L3*
(O.lmM)
Values
are mean + SEM of nt least
*Significantly student's
dTfferent
from
control
t test.
1403
three
separate (~~0.05)
were
although
high
similar
Site KD
two
In contrast, altered. The Moreover, the KD
1
max
the
1).
the
1 B
KD
to
The of
characteristics
decreased
DISCUSSION characteristics of
which
experiments
were unchanged (Table site were significantly site was decreased.
of
3). effect of
The binding
of this site also appeared to be significantly the effect was not statistically significant.
While the [3H]glibenclamide
the
is
experiments. as determined
by
found
Vol.
167,
No.
in other site in
3, 1990
BIOCHEMICAL
since only nucleotides.
coupled
a G-binding
to
to be performed The
BIOPHYSICAL
RESEARCH
the existence of (9,10), tissue is a novel finding.
tissues cardiac
be distinct by guanine need
AND
the
affinity suggests although
protein, in
concentration
low This
order
to
dependent
a low affinity These sites
site seems that this functional
rapid
sites
towards
filtration
a lower
Gpp[NH]p
effect
may indicate
the
site.
binding receptors
sites such
agonists The role
of the ATP-modulated of G-binding proteins
cardiac
state,
not
of high and low affinity nucleotide mediated
binding
in
affinity
cells
is typical as somatostatin
is
of
G-binding and galanin
manifested
low affinity shift part
There is also a in the affinity of this estimation of the affinity
existence The guanine
to be altered site may be experiments
is
methods.
significant, increase reflect a more accurate
binding appear to
be definitive.
a disappearance of a significant amount of the It may be that guanine nucleotides sites. binding
COMMUNICATIONS
binding of the
measurable large, but site which of the site states of disappearance
protein-coupled (15,16), which
K+ channel in pancreatic in the regulation of
as
with not may or this of
peptide are known
beta cells. this channel
unknown.
The data presented here suggest the cardiac channel may also be regulated by agonists whose receptor is guanine nucleotide dependent. While we have identified two [3H]glibenclamide binding sites in ventricular membranes, the relationship of these sites to the effects of glibenclamide on. cardiac
tissue
remains
to
be determined.
REFERENCES 1.
2. 3. 4. 5. 6. 7. 8. 9.
Sturgess. N.C., Ashford, M.L.J., Cook, D.L. and Hales, C.N. (1985) Lancet 2, 474-475. Schmid-Antomarchi, H., De Weille, J., Fosset, M., and Lazdunski. M. (1987) Biochem. Biophys. Res. Commun. 146, 2125. Schmid-Antomarchi, H., De Weille, J., Fosset, M., and Lazdunski, M. (1987) J. Biol. Chem. 262, 15840-15844. Noma. A. (1983) Nature 305, 147-148. Kakei, M., Noma. A., and Shibaski, P.R. (1985) J. physiol. (Lond.) 363, 441-462. Spruce, A.E., Standen, N.B., and Stanfield, P.R. (1985) Nature 316, 736-738. Ashford, M.L.J., Sturgess, N.C.. Trout, N.J., Gardner, N.J., and Hales, C.N. (1988) Pflugers Arch. 412, 297-304. Geisen, K., Hitzel, V., Okomonopoulos, R., Pwnter, J., Weyer, R.. and Summ, H.D. (1985) Arzniem. Forsch. 35, 707712. Gaines, K-L., Hamilton, S., and Boyd, A.E. (1988) J. Biol. Chem. 263, 2589-2592. 1404
Vol.
10.
11. 12. 13. 14. 15. 16.
167,
No.
3, 1990
BIOCHEMICAL
AND
BIOPHYSICAL
RESEARCH
COMMUNICATIONS
Fosset, M., De Weille, J.R., Green, R.D., Schmid-Antomarchi, H and Lazdunski, M. (1988) J. Biol. Chem. 263, 7933-7936. KaAtor, P-F., Coetzee, W.A., Dennis, S-C., and Opie, L.H. (1987) Circulation 76, 17. Wolleben, C.D., Sanguinetti, M.C., and Siegl, P.K.S. (1989) J. Mol. Cell Cardiol. 21, 783-788. Munson, P.J. and Rodbard, D. (1980) Anal. Biochem. 107, 220239. McPherson, G.A. (1985) J. Pharmacol. Meth. 14, 213-228. McKinney, M. and Barrett, R.W. (1989) Eur. J. Pharmacol. 162. 397-405. Lagny-Pourmir, I., Amiranoff, B., Lorinet, A.M., Tatemoto, K ., and Laburthe, Endocrinology 124, 2635-2641. M. (1989)
1405
167,
March
No.
30.
3, 1990
BIOCHEMICAL
AND
BIOPHYSICAL
RESEARCH
COMMUNICATIONS
Pages
1990
1400-1405
IDENTIFICATIOfJ OF HIGH AND LOW (GTP-SENSITIVE) AFFINITY [ HIGLIBENCLAMIDE BINDING SITES IN CARDIAC VENTRICULAR MEMBRANES J.F.
L.C.
French,
Cardiovascular
Riera
and J.G.
Sarmiento
Bristol-Myers Squibb, PRDD, Pharmacology, Wallingford,
CT 06492
Received February 1, 1990
SUMMARY: Glibenclamide is an antagonist of the ATP-modulated K+ channel in cardiac tissue. This study showed glibenclamide to bind to high (0.2 nM) and low (40 nM) affinity binding sites in canine ventricular membranes. Gpp[NH]p significantly altered the binding characteristics of the low affinity site, while those of the high affinity site were unchanged. This indicates independence of the two sites and suggests the low affinity site may be coupled to a Gbinding protein. Although we have identified two [3H]glibenclamide binding sites, the importance of these sites to the cardiac effects of glibenclamide remains to be determined. 0 1990Academic PESS,Inc.
The ATP-modulated beta
cells
(l-3),
and
cortical
K+ channel
cardiac
neurons
cells
(7).
has been identified (4-S),
The
most
skeletal potent
in pancreatic muscle
inhibitor
cells of
(6) this
channel to date is the sulfonylurea, glibenclamide. Binding sites for [3H]glibenclamide have been identified in insulinoma cells (8), pancreatic in chicken channel ischemia,
beta cells (9), cerebral cortex (8) and more recently and guinea pig heart microsomes (10). Inhibitors of this be potentially useful compounds during cardiac since they are capable of restoring normal or near normal
may
action shown
potential properties (10). Moreover, glibenclamide has been to prevent ischemia-induced ventricular fibrillation in isolated rat hearts (11-12). In the present study, we report the existence of two [3H]glibenclamide binding sites in canine heart ventricular membranes. These sites appear to be distinct since only the binding characteristics of the low affinity site are altered
by guanine
nucleotides. METHODS
Membrane Preparation. Dogs of either sex were anesthetized with pentobarbital (35 mg/kg) and their hearts rapidly removed and placed in ice-cold saline. The ventricles were dissected from the 0006-291X/90$1.50 Copyright All rights
0 1990 by Academic Press, Inc. of reproduction in any form reserved.
1400
Vol.
167,
No.
3, 1990
BIOCHEMICAL
AND
BIOPHYSICAL
RESEARCH
COMMUNICATIONS
atria and weighed. The ventricular tissue was then cut into small pieces and placed in ice-cold buffer solution (250 mM sucrose and 50 mM Tris-HCl, pH 7.4). The tissue was then homogenized four times in a blender at high speed for 20 set each. The homogenate was further homogenized by three treatments with a Brinkman Polytron for 10 set each at a speed setting of seven. The homogenate was then centrifuged at 1100 x g for 10 min. The resulting supernatant fraction was filtered through two layers of cheesecloth and then centrifuged at 12800 x g for 10 min. The supernatant fraction from this treatment was then centrifuged at 105000 x g for 35 min. The resulting pellet was resuspended in a small volume of buffer solution. The membrane preparations were rapidly frozen in liquid nitrogen and stored at -7O'C. Protein determinations were performed with Coomassie Protein Assay Reagent (Pierc Rockford, IL.) using bovine serum albumi as standard. ,f' HlGlibenclamide Bindinq Assavs. The [ Hlglibenclamide binding assays were performed in 50 mM Tris-HCl (pH 7.4) in a final volume of 0.5 ml. Each assay tube contained 250-500 ug of membrane protein and the desired concentration of [3H]glibenclamide (custom labeled by New England Nuclear, specific activity 50 Ci/mmole). The samples were incubated for 90 min at 22'C and then the reaction was terminated by dilution with 5 ml of ice-cold 50 mM Tris-HCl buffer and vacuum filtration on Whatman GF/C filters followed by quick washings of the filters three times with 5 ml of the same buffer. The filters were submerged in 5 ml scintillation fliud and the radioactivity was measured by liquid Scintillation spectroscopy. Specific binding of [3H]glibenclamide was defined as the amount of radioactivity displaced by 50 uM gliquidone, a structurally similar compound. Specific [3H]glibenclamide binding was proportional to protein content up to 1200 ug/ml. K and Bmax values were determined by the EBDA and LIGAND programs A 3,14). obtained from BoehringerMaterials. Gliqiudone was Ingelheim. Glibenclamide, Guanosine 5'-[B,y-imino]triphosphate (Gpp[NH]p) and all other chemical used were obtained from Sigma Chemical Co. (St. Louis, MO.).
Radioligand
RESULTS experiments
binding
the existence of [3H]glibenclamide ventricular membranes. Scatchard of [3H]glibenclamide ['H]glibenclamide constant a binding
(KD) site
binding
for the density
indicated sites
were
performed
high affinity (Bmax ) of 6.4
site was 0.22 + 0.9 fmols/mg
K,, for the second, lower affinity, site was affinity site expected the density of the lower greater (Bmax = 295 + 64 fmols/mg protein). sites, To verify the existence of two inhibition of and gliquidone
[3H]glibenclamide (Figure 2).
binding by these compounds = 0.9 + 0.02 and 10 + 0.3
to
determine
binding sites in canine analysis of the direct binding the existence of two The dissociation (Figure 1).
binding Inhibition was monophasic nM, respectively). 1401
& 0.07 nM with protein. The
40 f 11 nM. was considerably we
studied
As
the
by unlabeled glibenclamide of 0.3 nM [3H]glibenclamide and of high affinity In contrast, at
(Ki 3 nM
Vol.
167,
No.
BIOCHEMICAL
3, 1990
0
AND
BIOPHYSICAL
3
6
RESEARCH
COMMUNICATIONS
9
12
BOUND (fmole) Scatchard plot of ['Hlglibenclamide binding. Fioure 1. The ratio of bound ['Hlglibenclamide to free (B/F) ['Hlglibenclamide was plotted against the concentration of bound ['H]glibenclamide. Canine ventricular membranes were incubated for 90 min with increasing concentrations of ['Hlglibenclamide and binding was determined as described in "Methods." Each value was obtained from triplicate determinations. The experiment presented is representative of 5 experiments.
a biphasic displacement curve [3H]glibenclamide, These results are consistent with the identification sites
by direct Experiments
distinct of the of
A)
binding were
methods described above. carried out to determine
of two binding if
these were The ability
sites or affinity states of the same site. nonhydrolyzable GTP analog, Gpp[NH]p, to alter the binding was explored. ventricular membranes to
B)
100
0
1E :-10
was observed.
lE-9
lE-8
lE-7
4
lE-6
DRUG (M)
100
0
lE-9
I lE-8
lE-7
lE-6
lE-5
DRUG (M)
Figure 2. Inhibition of ]'H]glibenclamide binding by nonlabeled glibenclamide (0) and gliquidone (B) at (A) 0.3 and (B) 3 nM ["Hlglibenclamide. Percent specific binding in the absence of inhibitors is indicated. Each value is expressed as a mean + SEM of three experiments of triplicate determinations.
1402
lE-4
Vol.
167,
No.
3, 1990
BIOCHEMICAL
AND
BIOPHYSICAL
RESEARCH
COMMUNICATIONS
120-
1
Fisure 3. Gpp[NHlp. expressed determinations.
to was
of
significantly
binding by Each value of triplicate
inhibiting
, a concentration
both the high concentration
Gpp[NH]p on the 3 [ Hlglibenclamide performed
lOI30
CONCENTRATION (PM) Inhibition of 3 nM ['Hjglibenclamide Percent specific binding is indicated. as a mean + SEM of three experiments
Gpp[NH]p was capable 3 nM L3H]glibenclamide binds effect
100
lb
of
labeled
binding ligand
and low affinity sites (Figure dependent. To determine the
individual
binding
sites,
characteristics
saturation
in the presence
binding
of Gpp[NH]p.
of the high affinity site those of the lower affinity Bmax of the lower affinity
binding
site
appear
Table Site
be
affinity
to those
2 B max
Control
0.22+0.07
6.450.9
40.1f11.4
295t64
+GPP[NHIP
0.14+0.05
l3.0+1.2
5.7k1.6
20.5+2.L3*
(O.lmM)
Values
are mean + SEM of nt least
*Significantly student's
dTfferent
from
control
t test.
1403
three
separate (~~0.05)
were
although
high
similar
Site KD
two
In contrast, altered. The Moreover, the KD
1
max
the
1).
the
1 B
KD
to
The of
characteristics
decreased
DISCUSSION characteristics of
which
experiments
were unchanged (Table site were significantly site was decreased.
of
3). effect of
The binding
of this site also appeared to be significantly the effect was not statistically significant.
While the [3H]glibenclamide
the
is
experiments. as determined
by
found
Vol.
167,
No.
in other site in
3, 1990
BIOCHEMICAL
since only nucleotides.
coupled
a G-binding
to
to be performed The
BIOPHYSICAL
RESEARCH
the existence of (9,10), tissue is a novel finding.
tissues cardiac
be distinct by guanine need
AND
the
affinity suggests although
protein, in
concentration
low This
order
to
dependent
a low affinity These sites
site seems that this functional
rapid
sites
towards
filtration
a lower
Gpp[NH]p
effect
may indicate
the
site.
binding receptors
sites such
agonists The role
of the ATP-modulated of G-binding proteins
cardiac
state,
not
of high and low affinity nucleotide mediated
binding
in
affinity
cells
is typical as somatostatin
is
of
G-binding and galanin
manifested
low affinity shift part
There is also a in the affinity of this estimation of the affinity
existence The guanine
to be altered site may be experiments
is
methods.
significant, increase reflect a more accurate
binding appear to
be definitive.
a disappearance of a significant amount of the It may be that guanine nucleotides sites. binding
COMMUNICATIONS
binding of the
measurable large, but site which of the site states of disappearance
protein-coupled (15,16), which
K+ channel in pancreatic in the regulation of
as
with not may or this of
peptide are known
beta cells. this channel
unknown.
The data presented here suggest the cardiac channel may also be regulated by agonists whose receptor is guanine nucleotide dependent. While we have identified two [3H]glibenclamide binding sites in ventricular membranes, the relationship of these sites to the effects of glibenclamide on. cardiac
tissue
remains
to
be determined.
REFERENCES 1.
2. 3. 4. 5. 6. 7. 8. 9.
Sturgess. N.C., Ashford, M.L.J., Cook, D.L. and Hales, C.N. (1985) Lancet 2, 474-475. Schmid-Antomarchi, H., De Weille, J., Fosset, M., and Lazdunski. M. (1987) Biochem. Biophys. Res. Commun. 146, 2125. Schmid-Antomarchi, H., De Weille, J., Fosset, M., and Lazdunski, M. (1987) J. Biol. Chem. 262, 15840-15844. Noma. A. (1983) Nature 305, 147-148. Kakei, M., Noma. A., and Shibaski, P.R. (1985) J. physiol. (Lond.) 363, 441-462. Spruce, A.E., Standen, N.B., and Stanfield, P.R. (1985) Nature 316, 736-738. Ashford, M.L.J., Sturgess, N.C.. Trout, N.J., Gardner, N.J., and Hales, C.N. (1988) Pflugers Arch. 412, 297-304. Geisen, K., Hitzel, V., Okomonopoulos, R., Pwnter, J., Weyer, R.. and Summ, H.D. (1985) Arzniem. Forsch. 35, 707712. Gaines, K-L., Hamilton, S., and Boyd, A.E. (1988) J. Biol. Chem. 263, 2589-2592. 1404
Vol.
10.
11. 12. 13. 14. 15. 16.
167,
No.
3, 1990
BIOCHEMICAL
AND
BIOPHYSICAL
RESEARCH
COMMUNICATIONS
Fosset, M., De Weille, J.R., Green, R.D., Schmid-Antomarchi, H and Lazdunski, M. (1988) J. Biol. Chem. 263, 7933-7936. KaAtor, P-F., Coetzee, W.A., Dennis, S-C., and Opie, L.H. (1987) Circulation 76, 17. Wolleben, C.D., Sanguinetti, M.C., and Siegl, P.K.S. (1989) J. Mol. Cell Cardiol. 21, 783-788. Munson, P.J. and Rodbard, D. (1980) Anal. Biochem. 107, 220239. McPherson, G.A. (1985) J. Pharmacol. Meth. 14, 213-228. McKinney, M. and Barrett, R.W. (1989) Eur. J. Pharmacol. 162. 397-405. Lagny-Pourmir, I., Amiranoff, B., Lorinet, A.M., Tatemoto, K ., and Laburthe, Endocrinology 124, 2635-2641. M. (1989)
1405
