Acetylcholine receptors in human oocytes.

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Abstract
Neurotransmitter receptors have been studied by conventional electrophysiological techniques in the membrane of human ovarian oocytes isolated from ovarian fragments obtained from pre-menopausal women undergoing abdominal surgery for gynecological conditions. Ovarian oocytes respond to acetylcholine (ACh) concentrations as low as 10-10 M by hyperpolarizing the membrane and by concomitantly increasing input resistance, in a dose-dependent manner. The response lasts as long as the trasmitter is present in the extracellular fluid. No response is elicited by ionophoretically applied ACh. The ACh response has an apparent latency of less than 1 s and a reversal potential of about -12 mV. The response to ACh (10-8-10-3 M) is unaffected by curare (10-5-10-4 g/ml) and is blocked by atropine (10-6-10-4 g/ml). This indicates that ACh receptors in the human oocyte membrane are probably muscarinic in nature. No response is elicited by the amino acids glutamate, asparate, and glycine (up to 10-3 M), or by noradrenaline [norepinephrine], adrenaline [epinephrine] and 5-hydroxytryptamine (up to 10-3 M). Based on the response elicited by agents which activate parthenogenetic development in the oocytes of other mammals, it is suggested that the sperm-carried ACh might be involved in activation processes triggered by sperm-egg interaction.