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Articles by Abdul M. Ruknudin
Total Records ( 1 ) for Abdul M. Ruknudin
  Antoine Younes , Alexey E. Lyashkov , David Graham , Anna Sheydina , Maria V. Volkova , Megan Mitsak , Tatiana M. Vinogradova , Yevgeniya O. Lukyanenko , Yue Li , Abdul M. Ruknudin , Kenneth R. Boheler , Jennifer van Eyk and Edward G. Lakatta
  Spontaneous, rhythmic subsarcolemmal local Ca2+ releases driven by cAMP-mediated, protein kinase A (PKA)-dependent phosphorylation are crucial for normal pacemaker function of sinoatrial nodal cells (SANC). Because local Ca2+ releases occur beneath the cell surface membrane, near to where adenylyl cyclases (ACs) reside, we hypothesized that the dual Ca2+ and cAMP/PKA regulatory components of automaticity are coupled via Ca2+ activation of AC activity within membrane microdomains. Here we show by quantitative reverse transcriptase PCR that SANC express Ca2+-activated AC isoforms 1 and 8, in addition to AC type 2, 5, and 6 transcripts. Immunolabeling of cell fractions, isolated by sucrose gradient ultracentrifugation, confirmed that ACs localize to membrane lipid microdomains. AC activity within these lipid microdomains is activated by Ca2+ over the entire physiological Ca2+ range. In intact SANC, the high basal AC activity produces a high level of cAMP that is further elevated by phosphodiesterase inhibition. cAMP and cAMP-mediated PKA-dependent activation of ion channels and Ca2+ cycling proteins drive sarcoplasmic reticulum Ca2+ releases, which, in turn, activate ACs. This feed forward "fail safe" system, kept in check by a high basal phosphodiesterase activity, is central to the generation of normal rhythmic, spontaneous action potentials by pacemaker cells.
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