title: Different actions of calcium channel blocking agents on resting membrane conductance in developing skeletal muscle.
abstract: The effects of Co2+, Mn2+, and La3+ (2 mM) and verapamil (5 x 10(-6) M) on membrane conductance (Gm) and resting potential (Em) were studied in chick skeletal muscle fibres developing in culture. Cobalt and manganese had no effect on Gm at any time during myogenesis but verapamil caused a decrease in Gm in immature myotubes. This effect diminished with time and was absent by 3 days after myoblast fusion. Lanthanum caused an increase in Gm at all stages of development. All the agents studied caused a significant depolarization of Em. It is concluded that there is no resting calcium conductance in developing skeletal muscle but that there may be a resting sodium conductance which declines with maturation. Lanthanum may increase Gm by displacing membrane-bound calcium and destabilizing membrane structure. All the agents studied were thought to induce depolarization by an inhibitory action on (Na+ + K+)-ATPase.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002642:Chick Embryo; D003035:Cobalt / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects*; D007811:Lanthanum / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009132:Muscles / Q000187:drug effects / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors; D014700:Verapamil / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D007473:Ion Channels; D003035:Cobalt; D008345:Manganese; D007811:Lanthanum; D014700:Verapamil; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium