Single K channel currents in Schwann cells from normal and neurofibromatosis-affected damselfish

Damselfish neurofibromatosis is a naturally occurring disease of a tropical marine fish species. Affected fish exhibit peripheral nerve sheath tumors which contain morphologically abnormal Schwann cells (SC), similar to tumors encountered in the human disease neurofibromatosis type 1. Unitary A-type K channels in cell-attached membrane patches of SC were studied. Three different K channel conductances of approximately 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 from normal and tumored SC. Channel open time histograms were fit by a single exponential. The ranges of time constants for open times irrespective of conductance were 0.26-9.3 msec in patches from normal cells and 0.60-0.73 msec in patches from tumored cells. These ranges were not significantly different. Inactivation time constants from ensemble averages of single channel currents averaged 83 +/- 46 msec for normal SC and 44 +/- 26 msec for tumored SC, which were not significantly different. These results suggest that A-type K currents from fish SC are composed of channels exhibiting multiple conductances and a variety of inactivation rates, which may account for the range of inactivation observed in whole cell currents but whose activity in membrane patches may not be wholly applicable to the whole cell currents.