REGULATION BY AN EXTRACT OF EMBRYONIC CHICK BRAIN OF THE DENSITIES OFVOLTAGE-DEPENDENT NA-MUSCLE CELLS DURING THEIR DEVELOPMENT IN CULTURE( AND CA2+ CHANNELS IN EMBRYONIC CHICK SKELETAL)

We studied the chronic effects of a brain extract (BE) prepared from c hick embryonic brains on voltage-dependent Na+ channels (VDNCs) and Ca 2+ channels (VDCCs) during the development of chick skeletal muscle ce lls in culture. The maximum rates of rise of Na+ and Ca2+ action poten tials were measured electrophysiologically in an attempt to determine the effects of BE on the densities of these channels. The basic cultur e medium was supplemented with chick transferrin instead of whole-embr yo extract and skeletal muscle cells were grown in the absence or in t he presence of crude BE or fractionated BE. Long-term inclusion of BE to the culture medium increased the densities of both VDNCs and L-type VDCCs. By contrast, BE apparently decreased the density of T-type VDC Cs. Our results indicate that BE contains some protein(s) that has a n egative effect on the density of T-type VDCCs of skeletal muscle cells at a less differentiated stage and that this effect of BE is closely associated with subsequent regulation of the densities of VDNCs and L- type VDCCs. Possible roles of the influx of Ca2+ ions through T-type a nd L-type VDCCs in the control of the densities of VDNCs and L-type VD CCs are discussed. (C) 1998 Elsevier Science B.V. All rights reserved.