Voltage-dependent sodium and potassium channels in mammalian cultured Schwann cells.

Abstract

Cultured Schwann cells from sciatic nerves of newborn rabbits and rats were examined with patch-clamp techniques. In rabbit cells, single Na and K channels were detected with single channel conductances of 20 pS and 19 pS, respectively. Single Na channels have a reversal potential within 15 mV of ENa [Na equilibrium potential], are blocked by tetrodotoxin, and have rapid and voltage-independent inactivation kinetics. Single K channels show current reveral close to EK [K equilibrium potential] and are blocked by 4-aminopyridine. These results, and comparisons of single-channel and whole-cell data, show that these Schwann cells contain voltage-dependent Na and K channels that are similar in most respects to the corresponding channels in mammalian axonal membranes. Cultured rat Schwann cells also have Na channels, but a density about 1/10th that of rabbit cells, a result in agreement with saxitoxin binding experiments on axon-free sectioned nerves. Saxitoxin binding to cultured cells suggests that there are up to 25,000 Na channels in a single rabbit Schwann cell. In vivo Schwann cells in myelinated axons might act as a local source for Na channels at the nodal axolemma.