Mechanisms for the effects of acetylcholine on sodium transport in frog skin.

In frog skin (Rana temporaria) acetylcholine applied to the serosal surface produces either a sustained inhibiton or sustained stimulation of short-circuit current (SCC). The former effect is accompanied by a reduction and the latter by an increase in total tissue conductance. Both effects of acetylcholine can be accounted for, within experimental error, by changes in net sodium flux across the tissue. By use of selective agonists and antagonists it is concluded that acetylcholine interacts with muscarinic receptors in the serosal membrane. The effects of cholinoceptor agents are also seen with isolated epithelium. The stimulatory effect of acetylcholine is potentiated by theophylline and blocked by inhibitors of prostaglandin synthetase and by mepacrine. It is suggested that acetylcholine stimulates transport by liberating prostaglandins which may then activate adenylcyclase. The inhibitory effect of acetylcholine is correlated with a reduction in cyclic AMP content of the epithelium. Calcium appears to be an important determinant of the type of response seen eith acetylcholine, but the mechanism is not known.