DIFFERENCES IN A K-CURRENT IN SCHWANN-CELLS FROM NORMAL AND NEUROFIBROMATOSIS-INFECTED DAMSELFISH

Patch clamp techniques were used to study whole cell ionic currents in Schwann cells (SC) from a tropical marine fish, the bicolor damselfis h, Pomacentrus partitus. The bicolor damselfish is affected by a disea se termed damselfish neurofibromatosis (DNF), being developed as an an imal model of neurofibromatosis-type 1 (NF1) in humans. NF1 affects SC , fibroblasts, and perineurial cells. The sole depolarization-activate d ionic current present in cultured SC from normal fish peripheral ner ve and from neurofibromas of fish with induced or spontaneously occurr ing DNF was an inactivating K+ current (K current), with a strong depe ndence on the Nernst potential for K+ This K current activated at depo larizations to -40 mV and above and inactivated during a maintained te st pulse (0.2-1 s), but inactivation was significantly greater in tumo red SC. Both currents were inhibited by 4-aminopyridine (K-d similar t o 1 mM) and by dendrotoxin (15 mu M) but were insensitive to extracell ular tetraethyammonium (less than or equal to 150 mM), indicating that the whole cell currents were similar pharmacologically. The currents could be distinguished on the basis of their sensitivity to depolarize d holding potential, with normal cells less sensitive. Half-inactivati on of the current was -32 mV in normal cells and -38 mV in tumored cel ls. Inactivation curves constructed from the average normalized curren t for many SC were significantly different in normal and tumored cells . When the depolarized holding potential was maintained between test d epolarizations, greater voltage-dependent inactivation in tumored cell s was apparent. Normal cells maintained an average of 36% of peak curr ent at a holding voltage of -40 mV, while in tumored cells this averag e was 12%, a significant difference. (C) 1994 Wiley-Liss, Inc.