CHARACTERISTICS OF NA-CELLS CULTURED FROM FROG SCIATIC-NERVE( CURRENTIN SCHWANN)

Characteristics of voltage-dependent currents in cultured frog Schwann cells were investigated by the whole-cell clamp technique. An inward current was detectable at a membrane potential level more positive tha n -50 mV and reached a maximum value at about -10 mV, while no rectify ing channel was present. The inward current was carried by Na+ ions, b ecause the extrapolated reversal potential of the current agreed with the calculated EN., and the current was sensitive to tetrodotoxin. The membrane potential for half-maximal inactivation was -82 mV. The inac tivation curve indicated that more than 90% of the Na+ channels were i nactivated at the resting membrane potential, suggesting that the cult ured frog Schwann cells could not generate an action potential under p hysiological conditions. The time constant for the inactivation at a m aximum current was 5.3 ms (-10 mV, 13-degrees-C). The electrophysiolog ical characteristics of the Na+ current in the cultured frog Schwann c ells were compared with those in other tissues. This Na+ current was q uantitatively different from that observed in the amphibian node of Ra nvier but was similar to that in the mammalian Schwann or glial cells, especially in the more hyperpolarized half-maximal inactivation poten tial and in the slower inactivation time course. (C) 1994 Wiley-Liss, Inc.