Molecular bases of sympathetic innervation and developmental changes in ion channels

点击翻译按钮获取中文摘要

(1) SYMPATHETIC INNERVATION-MEDIATING PROTEIN Sympathetic nerve fibirs densely innervate expansor secundariorum muscle, but not skeletal muscle. In cilture sympathetic nerve fibers densely distributed on the substrate from expansor secundariorum but avoided distributing on the substrate from skeletal muscle. The protein which caused the dense distribution of sympathetic fibers as the substrate has been purified from heart cell conditioned medium. The most purified fraction showed single band with apparent molecular weight of 370,000 daltons on SDS-PAGE under non-reducing and reducing conditions. Antiserum was raised against the factor in heart cell conditioned medium. Subcutaneous injection of the antiserum into the chick inhibited the regeneration of adrenergic fibers following 6-hydroxydopamine-induced axotomy in peripheral tissues (heart, spleen, kidney and blood vessel). The results indicate that the protein may function in the process of reinnervation of lesioned sympathetic fiber … More s on target tissues in the chick.(2) DEVELOPMENTAL CHANGES OF VOLTAGE-SENSITIVE ION CHANNELS The whole-cell voltage-clamp technique was used to examine developmental changes in different types of Ba^<2+> currents through Ca^<2+> channels, Na^+ currents and inward rectifier K^+ currents in single fibres isolated from mouse flexor digitorum brevis muscle. The muscle fibres isolated on day 1 post-natal (P1) showed transient, I(Ca,T), and sustained currents, I(Ca,S). I(Ca,T) became undetectable by P17 and I(Ca,S) increased four-fold in the first 30 days. Denervation did not prevent the disappearance of I(Ca,T). Geographutoxin II(GTX) distinguished GTX-sensitive, I(Na,s), and GTX-resistant, I(Na,r) currents. I(Na,r) became undetectable by P16. I(Na,s) increased 15-fold in the first 20 days. In denervated muscle fibres I(Na,r) was increased above the level of normal fibers. Inwardly rectifying current was split into three components, I(steady-state), I(rise) and I(decay). I(decay) was observed throughout post-natal development. I(steady-state) and I(rise) became apparent after P12. Denervation depressed the increase of I(steady-state) and I(rise). We conclude that different types of ion channel currents in the muscle fibres undergo dramatic changes in their numbers as well as their properties by a few weeks after birth. Some changes are under the control of innervation, but others occur independent of innervation. Less