The calcium‐activated potassium conductance in guinea‐pig myenteric neurones

Abstract

Intracellular recordings were made from guinea pig myenteric neurons in vitro. From 1-60 action potentials were followed by an afterhyperpolarization, the amplitude and duration of which increased with the number of preceding action potentials. The afterhyperpolarization reversed its polarity at a membrane potential of -91 mV. This value changed by 58 mV when the K concentration of the perfusing solution was changed 10-fold. The afterhyperpolarization was abolished in Ca-free solutions. It was shortened in low Ca (1.2 mM) solutions and prolonged in solutions which contained high (5.0 mM) Ca concentrations, TEA [tetracethylammonium bromide] (1 mM) or caffeine (1 .mu.M). The conductance increase during the afterhyperpolarization (gK,Ca) was calculated from the amplitude of electrotonic potentials, taking advantage of the lack of membrane rectification in the range -60 to -90 mV. Peak gK,Ca increased as the number of action potentials was increased but was relatively independent of membrane potential in this range. gK,Ca declined with a time course which was single exponential (time constant 1.5-5 s) following 1-6 action potentials, and double exponential (time constants .apprx. 3 and 12 s) following 15-60 action potentials. Ca which enters the neuron during the action potential elevates the membrane K conductance. The time course of this conductance increase probably reflects the free intracellular Ca concentration and therefore describes the Ca sequestration or extrusion process.