SINGLE K CHANNEL CURRENTS IN SCHWANN-CELLS FROM NORMAL AND NEUROFIBROMATOSIS-AFFECTED DAMSELFISH

Damselfish neurofibromatosis is a naturally occurring disease of a tro pical marine fish species, Affected fish exhibit peripheral nerve shea th tumors which contain morphologically abnormal Schwann cells (SC), s imilar to tumors encountered in the human disease neurofibromatosis ty pe 1. Unitary A-type K channels in cell-attached membrane patches of S C were studied, Three different K channel conductances of approximatel y 5, 10, and 15 pS were present in both normal SC (n = 10) and tumored SC (n = 9), The variability in K channel conductance coincided with a large range of both mean open time and open probability in patches fr om normal and tumored SC, Channel open time histograms were fit by a s ingle exponential, The ranges of time constants for open times irrespe ctive of conductance mere 0.26-9.3 msec in patches from normal cells a nd 0.60-0.73 msec in patches from tumored cells, These ranges were not significantly different, Inactivation time constants from ensemble av erages of single channel currents averaged 83 +/- 46 msec for normal S C and 44 +/- 26 msec for tumored SC, which were not significantly diff erent, These results suggest that A-type K currents from fish SC are c omposed of channels exhibiting multiple conductances and a variety of inactivation rates, which may account for the range of inactivation ob served in whole cell currents but whose activity in membrane patches m ay not be wholly applicable to the whole cell currents. (C) 1997 Wiley -Liss, Inc.