DIVERSITY AND PROPERTIES OF CALCIUM-CHANNEL TYPES IN NG108-15 HYBRID-CELLS

We used an integral of the current-voltage relation as a new evaluatio n of Ca2+ current component composition in NG108-15 hybrid cells. We d etermined significant changes in the values and composition of Ca2+ cu rrents during cell differentiation. Only low-voltage-activated Ca2+ cu rrents could be observed in undifferentiated cells; after cell differe ntiation, high-voltage-activated currents appeared and the total Ca2current was increased about 30-fold. By pharmacological and biophysica l separation, we determined four main types of Ca2+ channels in differ entiated cells: approximately 50%, 20% and 17% of N, T and L types, re spectively, and 12% of residual current, which is insensitive to class ical blockers of low- and high-voltage-activated currents, with the ex ception of omega-conotoxin GVIA. All current components displayed kine tics and pharmacological properties similar to neuronal ones. We also established a significant Ca2+ dependence of omega-conotoxin GVIA to i nhibit N-type Ca2+ channels: 10 mM Ca2+ in bath solution reduced the t oxin efficacy to block N channels three-fold. The residual component f itted the properties of Q-type Ca2+ channels: it was sensitive to w-co notoxin GVIA and very similar to the T-type channel with respect to it s kinetics, however, the threshold of its activation was closer to the high-voltage-activated component (-40 mV). Our results show the funct ional diversity of Ca2+ channels and demonstrate, for the first lime, that presumably the Q type of an alpha(1A) family, which has biophysic al and pharmacological properties distinct From the previously describ ed T, L and N types in these cells, is co-expressed in NG108-15 cells. (C) 1998 IBRO. Published by Elsevier Science Ltd.