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Ca2+ release‐inducedinactivation of Ca2+current in ratventricular myocytes:evidence for localCa2+ signalling. James S.K. Sham1997 год

Ca2+ release‐induced inactivation of Ca2+ current in rat ventricular myocytes: evidence for local Ca2+ signalling.
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Аннотация: 1. Inactivation of Ca2+ current (ICa) induced by Ca2+ release from sarcoplasmic reticulum (SR) was studied in single rat ventricular myocytes using whole‐cell patch‐clamp and indo‐1 fluorescence measurement techniques. 2. Depolarizing pulses to 0 mV elicited large Ca2+ transients and ICa with biexponential inactivation kinetics. Varying SR Ca2+ loading by a 20 s pulse of caffeine showed that the fast component of ICa inactivation was dependent on the magnitude of Ca2+ release. 3. Inactivation of ICa induced by Ca2+ release was quantified, independently of voltage and Ca2+ entry, using a function termed fractional inhibition of ICa (FICa). The voltage relation of FICa had a negative slope, resembling that of single‐channel Ca2+ current (iCa) rather than the bell‐shaped current‐voltage (I‐V) relation of macroscopic ICa and Ca2+ transients. 4. Intracellular dialysis of myocytes with 10 mM EGTA (150 nM free [Ca2+]) had no effect on ICa inactivation induced by Ca2+ release, despite abolition of Ca2+ transients and cell contraction. Dialysis with 3 or 10 mM BAPTA (180 nM free [Ca2+]) attenuated FICa in a concentration‐dependent manner, with greater inhibition at positive than at negative potentials, consistent with more effective buffering of Ca2+ microdomains of smaller iCa. 5. Spatial profiles of [Ca2+] near an opened Ca2+ channel were simulated. [Ca2+] reached submillimolar levels at the mouth of the channel, and dropped steeply as radial distance increased. At any given distance from the channel, [Ca2+] was higher at negative than at positive potentials. The radii of Ca2+ microdomains were significantly reduced by 3 or 10 mM BAPTA, but not by 10 mM EGTA. 6. In conclusion, the distinctive voltage dependence and susceptibility of Ca2+ release‐induced ICa inactivation to fast and slow Ca2+ buffers suggests that the process is mediated through local changes of [Ca2+] in the vicinity of closely associated Ca2+ channels and ryanodine receptors.
Год издания: 1997
Авторы: James S.K. Sham
Издательство: Wiley
Источник: The Journal of Physiology
Ключевые слова: Cardiac electrophysiology and arrhythmias, Ion channel regulation and function, Neuroscience and Neural Engineering
Другие ссылки: The Journal of Physiology (HTML)
PubMed Central (HTML)
PubMed (HTML)