title: Depolarization of chick myotubes triggers the appearance of (+)-[3H]PN 200-110-binding sites.
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.
authors.affiliation: Department of Biochemical Pharmacology, Janssen Research Foundation, Beerse, Belgium.
authors.forename: P J
authors.initials: PJ
authors.lastname: Pauwels
authors.forename: H P
authors.initials: HP
authors.lastname: Van Assouw
authors.forename: J E
authors.initials: JE
authors.lastname: Leysen
mesh_terms: 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*
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D010069:Oxadiazoles; D011978:Receptors, Nicotinic; D009568:Nitrendipine; D017275:Isradipine