Abstract
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 MnCl2. MnCl2 had no significant effect on the efflux of 45Ca in the concentration range between 1.0mM and 20mM. In the presence of 1mM MnCl2, 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/cm2•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 MnCl2. This Ca content corresponding to 0.022p-mole/cm2•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.
