Depolarization of chick myotubes triggers the appearance of (+)-[3H]PN 200-110-binding sites

Mol Pharmacol. 1987 Dec;32(6):785-91.

Abstract

Regulation of the appearance of dihydropyridine-binding sites was studied in primary cultures of chick myotubes. Labeling of surface dihydropyridine-binding sites on intact myotubes at 37 degrees was achieved with (+)-[3H]PN 200-110. The appearance of the sites was prevented in a calcium-free medium using 1.8 mM EGTA, in accordance with the presumed Ca2+ dependency of the appearance of dihydropyridine-binding sites in skeletal muscle cells. Chronic treatment of myotubes with isoproterenol or various other drugs did not modulate either the Bmax or Kd value of the (+)-[3H]PN 200-110 binding to the membrane preparation of treated myotubes (control values were: Kd = 0.16 nm, Bmax = 556 fmol/mg of protein), suggesting a lack of heterologous regulation via beta-adrenergic receptor stimulation. However, depolarization of intact myotubes, either by 47 mM K+ or 10(-5) M veratridine, provoked a 3-fold increase in the Bmax value of (+)-[3H]PN 200-110 binding measured on the intact muscle cells without affecting the Kd value. The effect was reversed upon repolarization of the cells. Depolarizing conditions did not affect the binding on a membrane preparation of the myotubes. Hence, depolarization appeared to specifically trigger the appearance of (+)-[3H]PN 200-110 binding sites on intact myotubes; several hypotheses which could explain the involved mechanism are discussed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium Channel Blockers / metabolism*
  • Calcium Channels
  • Cells, Cultured
  • Chick Embryo
  • Isradipine
  • Muscles / analysis
  • Muscles / physiology*
  • Nitrendipine / metabolism
  • Oxadiazoles / metabolism*
  • Receptors, Nicotinic / analysis*

Substances

  • Calcium Channel Blockers
  • Calcium Channels
  • Oxadiazoles
  • Receptors, Nicotinic
  • Nitrendipine
  • Isradipine