title: CaMKII-dependent reactivation of SR Ca(2+) uptake and contractile recovery during intracellular acidosis.
abstract: In hearts, intracellular acidosis disturbs contractile performance by decreasing myofibrillar Ca(2+) response, but contraction recovers at prolonged acidosis. We examined the mechanism and physiological implication of the contractile recovery during acidosis in rat ventricular myocytes. During the initial 4 min of acidosis, the twitch cell shortening decreased from 2.3 +/- 0.3% of diastolic length to 0.2 +/- 0.1% (means +/- SE, P < 0.05, n = 14), but in nine of these cells, contractile function spontaneously recovered to 1.5 +/- 0.3% at 10 min (P < 0.05 vs. that at 4 min). During the depression phase, both the diastolic intracellular Ca(2+) concentration ([Ca(2+)](i)) and Ca(2+) transient (CaT) amplitude increased, and the twitch [Ca(2+)](i) decline prolonged significantly (P < 0.05). In the cells that recovered, a further increase in CaT amplitude and a reacceleration of twitch [Ca(2+)](i) decline were observed. The increase in diastolic [Ca(2+)](i) was less extensive than the increase in the cells that did not recover (n = 5). Blockade of sarcoplasmic reticulum (SR) function by ryanodine (10 microM) and thapsigargin (1 microM) or a selective inhibitor of Ca(2+)-calmodulin kinase II, 2-[N- (2-hydroxyethyl)-N-(4-methoxybenzenesulfonyl)] amino-N-(4-chlorocinnamyl)-N-methyl benzylamine (1 microM) completely abolished the reacceleration of twitch [Ca(2+)](i) decline and almost eliminated the contractile recovery. We concluded that during prolonged acidosis, Ca(2+)-calmodulin kinase II-dependent reactivation of SR Ca(2+) uptake could increase SR Ca(2+) content and CaT amplitude. This recovery can compensate for the decreased myofibrillar Ca(2+) response, but may also cause Ca(2+) overload after returning to physiological pH(i).
authors.affiliation: Division of Cardiology, Internal Medicine III, Hamamatsu University School of Medicine, Japan.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Nomura
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Satoh
authors.forename: Hajime
authors.initials: H
authors.lastname: Terada
authors.forename: Masaki
authors.initials: M
authors.lastname: Matsunaga
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Watanabe
authors.forename: Hideharu
authors.initials: H
authors.lastname: Hayashi
mesh_terms: D000138:Acidosis / Q000139:chemically induced / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000493:pharmacokinetics; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002245:Carbon Dioxide / Q000494:pharmacology; D002469:Cell Separation; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D011422:Propionates / Q000494:pharmacology; D051381:Rats; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D011422:Propionates; D002245:Carbon Dioxide; D012433:Ryanodine; D019284:Thapsigargin; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C029658:propionic acid; D002118:Calcium