title: Biphasic regulation of development of the high-affinity saxitoxin receptor by innervation in rat skeletal muscle.
abstract: Specific binding of 3H-saxitoxin (STX) was used to quantitate the density of voltage-sensitive sodium channels in developing rat skeletal muscle. In adult triceps surae, a single class of sites with a KD = 2.9 nM and a density of 21 fmol/mg wet wt  was detected. The density of these high-affinity sites increased from 2.0 fmol/mg wet wt to the adult value in linear fashion during days 2-25 after birth. Denervation of the triceps surae at day 11 or 17 reduced final saxitoxin receptor site density to 10.4 or 9.2 fmol/mg wet wt, respectively, without changing KD. Denervation of the triceps surae at day 5 did not alter the subsequent development of saxitoxin receptor sites during days 5-9 and accelerated the increase of saxitoxin receptor sites during days 9-13. After day 13, saxitoxin receptor development abruptly ceased and the density of saxitoxin receptor sites declined to 11 fmol/wg wet wt. These results show that the regulation of high-affinity saxitoxin receptor site density by innervation is biphasic. During the first phase, which is independent of continuing innervation, the saxitoxin receptor density increases to 47-57% of the adult level. After day 11, the second phase of development, which is dependent on continuing innervation, gives rise to the adult density of saxitoxin receptors.
mesh_terms: D000818:Animals; D001665:Binding Sites; D003714:Denervation; D007473:Ion Channels / Q000502:physiology; D009132:Muscles / Q000294:innervation* / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011955:Receptors, Drug / Q000502:physiology*; D012530:Saxitoxin / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D013779:Tetrodotoxin / Q000378:metabolism; D013997:Time Factors; D014316:Tritium
chemical_list: D007473:Ion Channels; D011955:Receptors, Drug; D014316:Tritium; D012530:Saxitoxin; D013779:Tetrodotoxin; D012964:Sodium