The effects of bathing sodium ions upon the intracellular sodium activity in calcium-free media and the calcium paradox of isolated ferret ventricular muscle.
Exposure of fine trabeculae isolated from the ferret right ventricle to media depleted of Ca2+, with a rapid perfusion system, causes a depolarization of the membrane and a rise in aiNa. This rise in aiNa is sigmoidally dependent upon the bathing free [Ca2+], is antagonized by reduction of the [Na]o, raised [Mg]o and PN200-110 but augmented by removal of Mg2+ or inhibition of the Na-pump. On repletion of Ca2+, the strength of the resulting contracture depends upon the transmembrane. Na-gradient at the moment of Ca-repletion. The effects of reduced [Na]o, during Ca-depletion, depend upon the cation used with replacement by Li much greater than choline greater than tetramethylammonium. These are determined by the change in the transmembrane gradient for Na+ and any additional action the replacing ion has upon the Ca-channels, the Na-pump and the Na/Ca exchange. The effects described are consistent with the hypothesis that the intensity of the calcium paradox in mammalian ventricle is primarily determined by the entry of Na+ through L-type Ca-channels during the period of Ca-depletion and the Ca-loading on Ca-repletion due to the effect of the raised aiNa upon the Na/Ca exchange.
Bhojani
I H
IH
Laboratory of Cellular Cardiology, Department of Physiology, School of Veterinary Sciences, Bristol, UK.
Chapman
R A
RA
D000109:Acetylcholine / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002335:Carnivora / Q000502:physiology*; D003470:Culture Media / Q000378:metabolism / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005289:Ferrets / Q000502:physiology*; D006352:Heart Ventricles / Q000187:drug effects* / Q000378:metabolism; D008094:Lithium / Q000378:metabolism / Q000494:pharmacology; D008839:Microelectrodes; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology* / Q000502:physiology; D016276:Ventricular Function
D002121:Calcium Channel Blockers; D003470:Culture Media; D008094:Lithium; D012964:Sodium; D000109:Acetylcholine; D002118:Calcium