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A cardiac dihydropyridine receptor II‐III loop peptide inhibits resting Ca 2+ sparks in ferret ventricular myocytes
Author(s) -
Li Yanxia,
Bers Donald M.
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.0017k.x
Subject(s) - ryanodine receptor , chemistry , biophysics , caffeine , endoplasmic reticulum , myocyte , dihydropyridine , voltage clamp , gating , calcium , medicine , membrane potential , biochemistry , biology , organic chemistry
1 We studied the effect of a peptide (Ac‐10C) on cardiac ryanodine receptor (RyR) opening. This decapeptide (KKERKLARTA) is a fragment of the cardiac dihydropyridine receptor (DHPR) from the cytosolic loop between the second and third transmembrane domains (II‐III loop). Studies were carried out in ferret ventricular myocytes by simultaneously applying ruptured‐patch voltage clamp and line‐scan confocal microscopy with fluo‐3 to measure intracellular [Ca 2+ ] ([Ca 2+ ] i ) and Ca 2+ sparks. 2 Inclusion of Ac‐10C in the dialysing pipette solution inhibited resting Ca 2+ spark frequency (due to diastolic RyR openings) by > 50 %. This occurred without changing sarcoplasmic reticulum (SR) Ca 2+ content, which was measured via the caffeine‐induced Ca 2+ transient amplitude and the caffeine‐induced Na + ‐Ca 2+ exchange current ( I NCX ) integral. Ac‐10C also reduced slightly the size of Ca 2+ sparks. 3 Ac‐10C did not alter either resting [Ca 2+ ] i (assessed by indo‐1 fluorescence) or DHPR gating (measured as L‐type Ca 2+ current). 4 The SR Ca 2+ fractional release was depressed by Ac‐10C at relatively low SR Ca 2+ content, but not at higher SR Ca 2+ content. 5 A control scrambled peptide (Ac‐10CS) did not alter any of the measured parameters (notably Ca 2+ spark frequency or SR Ca 2+ fractional release). Thus, the Ac‐10C effects may be sequence or charge distribution specific. 6 Our results suggest an inhibitory regulation of RyRs at rest via the cardiac DHPR II‐III loop N‐terminus region. The mechanism of the effect and whether this interaction is important in cardiac excitation‐contraction coupling (E‐C coupling) per se , requires further investigation.