Acetylcholine receptors in monkey and rabbit oocytes.

Membrane potential responses to acetylcholine (ACh, 10(-7)-10(-3 M) were investigated in monkey and rabbit ovarian oocytes. In monkey oocytes ACh most commonly elicited a short-latency hyperpolarization concomitant with a decreased membrane input resistance (Rin). Under voltage-clamp short-latency ACh currents had an equilibrium potential of approximately -40 mV. In rabbit oocytes responses to ACh consisted of an increase in Rin or of a depolarization with an equilibrium potential of approximately -15 mV. Curare, hexamethonium, and atropine (10(-5)-10(-3) M) did not block these ACh responses. Thus, the oocyte membrane in the rabbit contains ACh receptors that cannot be classified as either muscarinic or nicotinic.