Regulation by an extract of embryonic chick brain of the densities of voltage-dependent Na + and Ca 2+ channels in embryonic chick skeletal muscle cells during their development in culture

Abstract

We studied the chronic effects of a brain extract (BE) prepared from chick embryonic brains on voltage-dependent Na + channels (VDNCs) and Ca 2+ channels (VDCCs) during the development of chick skeletal muscle cells in culture. The maximum rates of rise of Na + and Ca 2+ action potentials were measured electrophysiologically in an attempt to determine the effects of BE on the densities of these channels. The basic culture medium was supplemented with chick transferrin instead of whole-embryo extract and skeletal muscle cells were grown in the absence or in the 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 VDCCs. Our results indicate that BE contains some protein(s) that has a negative 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 Ca 2+ ions through T-type and L-type VDCCs in the control of the densities of VDNCs and L-type VDCCs are discussed.