title: Ca2+ sparks and cellular distribution of ryanodine receptors in developing cardiomyocytes from rat.
abstract: Although abundant ryanodine receptors (RyRs) exist in cardiomyocytes from newborn (NB) rat and despite the maturity of their single-channel properties, the RyR contribution to excitation-contraction (E-C) coupling is minimal. Immature arrangement of RyRs in the Ca(2+) release site of the sarcoplasmic reticulum and/or distant RyRs location from the sarcolemmal Ca(2+) signal could explain this quiescence. Consequently, Ca(2+) sparks and their cellular distribution were studied in NB myocytes and correlated with the formation of dyads and transverse (T) tubules. Ca(2+) sparks were recorded in fluo-4-loaded intact ventricular myocytes acutely dissociated from adult and NB rats (0-9 days old). Sparks were defined/compared in the center and periphery of the cell. Co-immunolocalization of RyRs with dihydropyridine receptors (DHPR) was used to estimate dyad formation, while the development of T tubules was studied using di-8-ANEPPS and diIC12. Our results indicate that in NB cells, Ca(2+) sparks exhibited lower amplitude (1.7+/-0.5 vs. 3.6+/-1.7 F/F(0)), shorter duration (47+/-3.2 vs. 54.1+/-3 ms), and larger width (1.7+/-0.8 vs. 1.2+/-0.4 microm) than in adult. Although no significant changes were observed in the overall frequency, central sparks increased from approximately 60% at 0-1 day to 82% at 7-9 days. While immunolocalization revealed many central release sites at 7-8 days, fluorescence labeling of the plasma membrane showed less abundant internal T tubules. This could imply that although during the first week, release sites emerge forming dyads with DHPR-containing T tubules; some of these T tubules may not be connected to the surface, explaining the RyR quiescence during E-C coupling in NB.
authors.affiliation: Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA.
authors.forename: Rose M
authors.initials: RM
authors.lastname: Snopko
authors.affiliation: Department of Molecular Biophysics and Physiology, Rush University, Chicago, IL 60612, USA.
authors.forename: Josefina
authors.initials: J
authors.lastname: Ramos-Franco
authors.affiliation: Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Di Maio
authors.affiliation: Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA.
authors.forename: Kimberly L
authors.initials: KL
authors.lastname: Karko
authors.affiliation: Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Manley
authors.affiliation: Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA.
authors.forename: Erika
authors.initials: E
authors.lastname: Piedras-Rentería
authors.affiliation: Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA. Electronic address: rmejia@midwestern.edu.
authors.forename: Rafael
authors.initials: R
authors.lastname: Mejía-Alvarez
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002232:Carbocyanines / Q000494:pharmacology; D005260:Female; D005456:Fluorescent Dyes / Q000494:pharmacology; D008297:Male; D011726:Pyridinium Compounds / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012508:Sarcolemma / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013997:Time Factors
chemical_list: C089669:1-(3-sulfonatopropyl)-4-(beta-(2-(di-n-octylamino)-6-naphthyl)vinyl)pyridinium betaine; D002232:Carbocyanines; D005456:Fluorescent Dyes; D011726:Pyridinium Compounds; D019837:Ryanodine Receptor Calcium Release Channel; C097511:didodecylindocarbocyanine; D002118:Calcium