title: Altered distribution of ICa impairs Ca release at the t-tubules of ventricular myocytes from failing hearts.
abstract: In mammalian cardiac ventricular myocytes, Ca influx and release occur predominantly at t-tubules, ensuring synchronous Ca release throughout the cell. Heart failure is associated with disrupted t-tubule structure, but its effect on t-tubule function is less clear. We therefore investigated Ca influx and release at the t-tubules of ventricular myocytes isolated from rat hearts ~18weeks after coronary artery ligation (CAL) or corresponding Sham operation. L-type Ca current (ICa) was recorded using the whole-cell voltage-clamp technique in intact and detubulated myocytes; Ca release at t-tubules was monitored using confocal microscopy with voltage- and Ca-sensitive fluorophores. CAL was associated with cardiac and cellular hypertrophy, decreased ejection fraction, disruption of t-tubule structure and a smaller, slower Ca transient, but no change in ryanodine receptor distribution, L-type Ca channel expression, or ICa density. In Sham myocytes, ICa was located predominantly at the t-tubules, while in CAL myocytes, it was uniformly distributed between the t-tubule and surface membranes. Inhibition of protein kinase A with H-89 caused a greater decrease of t-tubular ICa in CAL than in Sham myocytes; in the presence of H-89, t-tubular ICa density was smaller in CAL than in Sham myocytes. The smaller t-tubular ICa in CAL myocytes was accompanied by increased latency and heterogeneity of SR Ca release at t-tubules, which could be mimicked by decreasing ICa using nifedipine. These data show that CAL decreases t-tubular ICa via a PKA-independent mechanism, thereby impairing Ca release at t-tubules and contributing to the altered excitation-contraction coupling observed in heart failure.
authors.affiliation: School of Physiology and Pharmacology, Medical Sciences Building, University of Bristol, Bristol BS8 1TD, UK.
authors.forename: Simon M
authors.initials: SM
authors.lastname: Bryant
authors.affiliation: School of Physiology and Pharmacology, Medical Sciences Building, University of Bristol, Bristol BS8 1TD, UK.
authors.forename: Cherrie H T
authors.initials: CH
authors.lastname: Kong
authors.affiliation: School of Physiology and Pharmacology, Medical Sciences Building, University of Bristol, Bristol BS8 1TD, UK.
authors.forename: Judy
authors.initials: J
authors.lastname: Watson
authors.affiliation: School of Physiology and Pharmacology, Medical Sciences Building, University of Bristol, Bristol BS8 1TD, UK.
authors.forename: Mark B
authors.initials: MB
authors.lastname: Cannell
authors.affiliation: School of Physiology and Pharmacology, Medical Sciences Building, University of Bristol, Bristol BS8 1TD, UK. Electronic address: a.james@bristol.ac.uk.
authors.forename: Andrew F
authors.initials: AF
authors.lastname: James
authors.affiliation: School of Physiology and Pharmacology, Medical Sciences Building, University of Bristol, Bristol BS8 1TD, UK. Electronic address: clive.orchard@bristol.ac.uk.
authors.forename: Clive H
authors.initials: CH
authors.lastname: Orchard
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000096:biosynthesis* / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D006333:Heart Failure / Q000378:metabolism* / Q000473:pathology; D006352:Heart Ventricles / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D007546:Isoquinolines / Q000008:administration & dosage; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000473:pathology; D018408:Patch-Clamp Techniques; D051381:Rats; D013449:Sulfonamides / Q000008:administration & dosage
chemical_list: D020746:Calcium Channels, L-Type; D007546:Isoquinolines; D013449:Sulfonamides; D017868:Cyclic AMP-Dependent Protein Kinases; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D002118:Calcium
keywords: Ca imaging; Heart failure; t-tubules