MECHANISM
OF
CONTRACTILE
IN Nobuyoshi
ISOLATED
YOSHIDA,
RESPONSE RAT
Kohtaro
and Hiroshi
TO
Mn
ION
RECTUM
TANIYAMA,
Hiromasa
ARAKI
MATSUMOTO'
Department of Pharmacology, Kobe University School of Medicine, Ikuta-ku, Kobe 650, Japan Accepted December 27, 1976
It is generally membrane
accepted
(1-4).
bind to troponin
(5).
storage sites in rabbit
Shibata
Mn ion inhibits
the transport
that Mn ion accelerated
through
the
cell
the release of Ca from
of MnCl., to normal medium caused a transient
the mechanism
to the mobilization
(1) reported
of Ca
that Mn ion has the ability to
aorta.
Since the addition rat rectum,
that
On the other hand, it has been proposed
of contraction
contraction
induced by Mn was investigated
in isolated
herein in relation
of Ca.
Male rats (200-250 g) were sacrificed by a blow on the neck.
The rectum was removed,
dissected and strips, approx.
I cm long, were fixed vertically with a load of 0.9-1.0 g in the
preparation
30 ml of nutrient
bath containing
5.6; CaC12, 2.2; glucose, on a smoked at 29
5.6; NaHCO3,
paper with a magnification
1°C and continuously
were allowed Ca-free
to equilibrate
solution
bubbled
medium,
of approx.
with a mixture of 95
about
was reduced
3 min exposure
(Fig. 1).
It is considered
that
was postulated
peated
medium,
treatments
later (Fig. 1). for 5.5
by 0.8 mM 0.8 mM
Preparations
solution
were begun.
except that
CaCl2
contraction,
The contraction
and a return to by 0.8 11-IMMn,
by hypertonic
as compared
81 mM K,
with that in normal
by a Ca-free
medium,
was usually observed
a transient 2 min later.
is due to release of Ca from storage sites, such as
Mn Would Mn-induced
findings in guinea
be attenuated contraction
3 min
pig ileum. after
the
was gradually
These results
which
Therefore, Ca
decreased
of 30 min and disappeared
by 0.8 mM Mn were not influenced
10-0 mM atropine
10-4 mM acetylcholine.
,;Present address:
was replaced
to the initial tonus
with 0.8 mM Mn at an interval 5
CO,,.
before experiments
contraction
medium,
et al. (6) for their
These contractions
10 min with
2 min later.
to Ca-free
this contraction
by Hurwitz
the contraction In Ca-free
and a return
was maintained
as Locke's
of maximal
When the bath medium
appeared
were recorded
The solution
mM) caused a transient
50%; of the magnitude
contraction
NaCI, 154; KCI.
was added.
Mn (0.008-8.0
which was approx.
medium
solution: contractions
02 and 5
media,
in the same fashion
the initial tonus was usually observed
after
(Locke's Isotonic
10 times.
for 90 min in normal
was prepared
was omitted and 0.01 mM GEDTA In normal
solution
4.8 (mM)).
completely
inhibited
removal. by re 90 min
by pretreatment
the contraction
by
suggest that Mn ion may induce the release of
Doshisha Women's College . Kyoto 602, Japan
Fic.
I.
Modification
of Mn (0.8 mM)-induced
contraction
in Ca-free
Medium.
In
normal medium, Mn-induced contraction was compared with the maximal con traction by hypertonic K (81 mM). After 3 min exposure to Ca-free medium, treatments for 2 min with Mn (0.8 mM) were repeated at an interval of 30 min. After Mn-induced contraction had disappeared in Ca-free of 27 mM K was repeated for 3 min at 30 min intervals. which
27 mM
Mn together
K-induced
contraction
had disappeared,
with 27 mM
K produced
a contraction,
Ca from storage sites.
Furthermore,
tonic 27 mM K disappeared 27 mM K caused producible
in Ca-free medium,
a transient
(Fig.
I ).
would accelerate
contraction,
Therefore,
by 5.5
reduced
preparation
by pretreatment
in which the contraction the addition a contraction.
attributed
to the influx of Ca (Table
by hypertonic
These contractions 1).
magnitudes
taken as 100 in each control.
of
Furthermore,
27 mM K had disappeared
but
a contraction,
contractions
by
while the same concentration
rat rectum.
Osa (8) has demonstrated
of contractions
agonists
(P
in control
by acetylcholine
preparations
0.01).
(ACh),
were
respectively. Values are indicated as percent of the magnitude Mn (0.8 mM) was applied by pretreatment for 10 min.
contraction
had disappeared.
No. of preparations
* Values used, 5.
induced
reports.
The magnitude of Ca-induced contraction was determined in Ca-free containing hypertonic 27 mM K in the preparation in which hypertonic K-induced
in Ca-free
by 0.8 mM Mn and such was
with numerous
the magnitudes
in the
with 27 mM K to Ca-free mediumn
Thus, Mn ion indeed inhibits contractions
action in isolated
TABLE I. Effect of Mn on K and Ca
control
elements,
and 13.5 mM K, which were
were inhibited
agents and such is consistent
an antispasmodic
The
contractile
with
was not re
sites and by the passive influx of Ca (7), were
In the present study, Mn ion produced Mn cawed
the
contraction
for 10 min with 0.8 mM Mn.
of 2 mM Ca or 2 mM Ca together
produced
by contracting
activate
by hyper
of 0.8 mM Mn together
the transient
10-4 mM acetylcholine
by the release of Ca from storage
significantly
medium,
not
of 0.8 mM
in which the contraction
the addition
although
Mn would
the addition
which was not reproducible.
the release of Ca from. storage sites.
The phasic contractions produced
in the preparation
medium, the addition In the preparation in
significantly
medium 27 mM
different
from
of that
the occupation membrane
by Mn of the outer surface of the membrane
to Ca, whereas Mn penetrates
of the membrane,
resulting
and guinea pig ileum.
in inhibition
the membrane
of Ca sequestration
It has been reported
membrane
using the Ca ion transport
penetrates
the membrane
inhibits the permeability
of the
and then binds to the inner structure in pregnant
mouse myometrium
that Mn ions are taken up by the chorioallantoic
pathway
of rat rectum, thereby
(9).
Thus,
influencing
it is possible
that Mn ion also
the inner structure,
presumably
at the area of Ca storage sites. REFERENCES 1) SHIBATA,S.: Canad. J. Physiol. Phcnmacol. 47, 827 (1969); 2) KEENS,J.J., SEIDEL, C.L. AND BOHR, D.F.: Proc. Soc. exp. Biol. Med. 139, 1083 (1972); 3) KATASE,T. AND TOMITA,T.: J. Physiol. 224, 489 (1972); 4) OSA, T.: Japan. J. Physiol. 23, 113 (1973); 5) Fucxs, F.: Biochim. Biophys. Acta 245, 221 (1971); 6) HURWITZ, L., JOINER, P.D. AND VON HAGEN, S.: Am. J. Physiol. 213, 1299 (1967); 7) TANIYAMA,K., ARAKI, H., MAEDA, M., CHENG, J.T. AND MATSUMOTO,H.: Folia pharmacol. japon. 72, 105 (1976) (in Japanese): 8) OSA, T.: Japan. J. Physiol. 24, 101 (1974); 9) ARMBRECHT,H.J., TiREPKA, A.R. AND GUNTIii, T.E.: Biochint. Biophys. Acta 426, 547 (1976)