Depolarization of chick myotubes triggers the appearance of (+)-[3H]PN 200-110-binding sites.
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.
Pauwels
P J
PJ
Department of Biochemical Pharmacology, Janssen Research Foundation, Beerse, Belgium.
Van Assouw
H P
HP
Leysen
J E
JE
D000818:Animals; D002121:Calcium Channel Blockers / Q000378:metabolism*; D015220:Calcium Channels; D002478:Cells, Cultured; D002642:Chick Embryo; D017275:Isradipine; D009132:Muscles / Q000032:analysis / Q000502:physiology*; D009568:Nitrendipine / Q000378:metabolism; D010069:Oxadiazoles / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000032:analysis*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D010069:Oxadiazoles; D011978:Receptors, Nicotinic; D009568:Nitrendipine; D017275:Isradipine