Cyclic GMP mimics the muscarinic response in Xenopus oocytes: identity of ionic mechanisms.

Abstract

Acetylcholine (AcCho) elicits 4 distinct membrane responses in Xenopus oocytes; the responses can be studied by using the voltage clamp technique. The fastest of the resonses, a transient inward current (D1 response), is muscarinic, being evoked by oxotremorine and blocked by atropine but not by curare or hexmethonium. The action of AcCho is cooperative, 3 transmitter-receptor complexes being required to cause a membrane conductance change, and the dose-response curve in most cases can be fitted by an equation assuming the existence of 2 binding sites with an affinity ratio of .apprx. 11. cGMP and its 8-bromo and dibutyryl derivatives cause a response similar to D1 in both its time course and the underlying ionic mechanism. The nucleotide-generated response has a smaller amplitude than the AcCho-generated D1.