Serum factor induces selective increase in Na-channel expression in cultured skeletal muscle.
We have examined effects of horse serum (HS) and various fractions (1 million-1M, 300K, 100K, and 30K nominal molecular weight limit) obtained by ultrafiltration on expression of TTX-sensitive Na-channels and on activities of the Na-K pump and glucose transport systems in cultured myotubes obtained from 1-2-day-old neonatal rat pups. Five-day-old cells were transferred to serum-free medium with no hormone or growth factor supplements (DMEM) for 24 hr and then treated with the various serum fractions for 48 hr. Measurements were made of specific [3H]-saxitoxin (STX) binding, action potential properties, 86Rb-uptake and 2-deoxyglucose (2-DG) uptake. HS significantly increased all parameters compared to DMEM (increases in STX-binding, 69%; Rb-uptake, 65%; 2-DG uptake, 93%). Results of treatment with the separate fractions showed that the 300K fraction caused a significantly greater increase in STX-binding than either HS or the other fractions. In contrast, the increases in Rb and 2-DG uptakes induced by the different fractions were not different from that obtained with HS. We conclude that serum contains a factor that selectively increases expression of TTX-sensitive Na-channels in skeletal muscle.
Brodie
C
C
Department of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel.
Sampson
S R
SR
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001798:Blood Proteins / Q000494:pharmacology*; D002352:Carrier Proteins / Q000502:physiology; D002478:Cells, Cultured; D003847:Deoxyglucose / Q000493:pharmacokinetics; D006133:Growth Substances / Q000494:pharmacology; D009132:Muscles / Q000166:cytology* / Q000502:physiology / Q000648:ultrastructure; D051381:Rats; D012414:Rubidium Radioisotopes / Q000493:pharmacokinetics; D012530:Saxitoxin / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*; D028021:Sodium-Potassium-Chloride Symporters; D013779:Tetrodotoxin / Q000494:pharmacology
D001798:Blood Proteins; D002352:Carrier Proteins; D006133:Growth Substances; D012414:Rubidium Radioisotopes; D015222:Sodium Channels; D028021:Sodium-Potassium-Chloride Symporters; D012530:Saxitoxin; D013779:Tetrodotoxin; D003847:Deoxyglucose