title: Contribution of Ca(2+) transporters to relaxation in intact ventricular myocytes from developing rats.
abstract: The relative contributions of Ca(2+) transporters to intracellular Ca(2+) concentration ([Ca(2+)](i)) decline associated with twitch relaxation were analyzed in intact ventricular myocytes from developing and adult rats. This was accomplished by estimation of individual integrated Ca(2+) fluxes with the use of kinetic parameters calculated from [Ca(2+)](i) measurements during twitches and caffeine-evoked contractures, and from myocardial passive Ca(2+) buffering data. Our main findings were the following: 1) twitch relaxation and [Ca(2+)](i) decline were significantly slower during the first postnatal week than in adults, 2) inhibition of sarcoplasmic reticulum (SR) Ca(2+) accumulation resulted in faster [Ca(2+)](i) decline in young cells than in adult cells, 3) the contributions of the SR Ca(2+) uptake and Na(+)/Ca(2+) exchange (NCX) to twitch relaxation increased from ~75 to 92%, and decreased from 24 to 5%, respectively, from birth to adulthood, and 4) Ca(2+) transport by the sarcolemmal Ca(2+)-ATPase was apparently increased in neonates. Our data indicate that despite a marked increase in NCX contribution to cell relaxation in immature rats, the SR Ca(2+)-ATPase appears to be the predominant transporter responsible for relaxation-associated [Ca(2+)](i) decline from birth to adulthood.
authors: Centro de Engenharia Biomédica and Departamento de Engenharia Biomédica/ Faculdade de Engenharia Elétrica e de Computação, Universidade Estadual de Campinas, Campinas 13083-971, Brazil. rosana@ceb.unicamp.br
authors: Rosana A
authors: RA
authors: Bassani
authors: José W M
authors: JW
authors: Bassani
mesh_terms: D000375:Aging; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000502:physiology; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D006321:Heart / Q000254:growth & development*; D006352:Heart Ventricles / Q000166:cytology; D007476:Ionophores / Q000494:pharmacology; D007700:Kinetics; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D016276:Ventricular Function
chemical_list: D002135:Calcium-Binding Proteins; D007476:Ionophores; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D000252:Calcium-Transporting ATPases; D002118:Calcium