Spontaneous muscarinic suppression of the Ca-activated K-current in bullfrog sympathetic neurons.

Neurons in bullfrog sympathetic ganglia were voltage-clamped using a single microelectrode. A prolonged outward current which was identified as the Ca-activated K-current secondary to a transient Ca entry through voltage-operated channels was shortened by oxotremorine. An inward Ca-current was not significantly depressed by oxotremorine. It was suggested that muscarinic agonists accelerate the re-closure of K-channels either directly or secondarily via their effects on an intracellular sequestration process of Ca ions. It was also suggested that a small amount of acetylcholine only sufficient to cause a miniature synaptic current via nicotinic receptors could shorten the Ca-activated K-current via muscarinic receptors.