title: Relaxation of isolated ventricular cardiomyocytes by a voltage-dependent process.
abstract: Cell contraction and relaxation were measured in single voltage-clamped guinea pig cardiomyocytes to investigate the contribution of sarcolemmal Na+-Ca2+ exchange to mechanical relaxation. Cells clamped from -80 to 0 millivolts displayed initial phasic and subsequent tonic contractions; caffeine reduced or abolished the phasic and enlarged the tonic contraction. The rate of relaxation from tonic contractions was steeply voltage-dependent and was significantly slowed in the absence of a sarcolemmal Na+ gradient. Tonic contractions elicited in the absence of a Na+ gradient promptly relaxed when external Na+ was applied, reflecting activation of Na+-Ca2+ exchange. It appears that a voltage-dependent Na+-Ca2+ exchange can rapidly mechanically relax mammalian heart muscle.
authors.affiliation: Nora Eccles Harrison Cardiovascular Research and Training Institute, Salt Lake City, UT.
authors.forename: J H
authors.initials: JH
authors.lastname: Bridge
authors.forename: K W
authors.initials: KW
authors.lastname: Spitzer
authors.forename: P R
authors.initials: PR
authors.lastname: Ershler
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D004558:Electric Stimulation; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects; D010477:Perfusion; D012508:Sarcolemma / Q000187:drug effects / Q000502:physiology
chemical_list: D002110:Caffeine