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)

Mechanism of contractile response to Mn ion in isolated rat rectum.

MECHANISM OF CONTRACTILE IN Nobuyoshi ISOLATED YOSHIDA, RESPONSE RAT Kohtaro and Hiroshi TO Mn ION RECTUM TANIYAMA, Hiromasa ARAKI MAT...
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