Ca uptake and efflux in the smooth muscle cell of guinea-pig taenia coli were estimated in the normal Krebs solution and in Krebs solution containing MnCl
2. MnCl
2 had no significant effect on the efflux of
45Ca in the concentration range between 1.0mM and 20mM. In the presence of 1mM MnCl
2, adrenaline (up to 2.5×10
-5g/ml) and tetrodotoxin (up to 2.5×10
-3g/ml) had no significant effect on Ca efflux. But acetylcholine (up to 2.5×10
-3g/ml) was found to increase the
45Ca efflux coincidentally with the tension development. Ca influx in normal NaCl Krebs solution was estimated to be 0.135p-mole/cm
2•sec, and it was increased by 1.5 to 2 times in Na free sucrose Krebs solution. About 15% of total Ca influx was suppressed by 1.0mM MnCl
2. This Ca content corresponding to 0.022p-mole/cm
2•sec was tentatively attributed to the extra entry of Ca by the generation of action potential. But this amount proved to correspond to only 2% of the theoretically calculated necessary amount of divalent cation inflow accompanying the generation of action potential.
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