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J Physiol Volume 586, Number 16, 3839-3854, August 15, 2008 DOI: 10.1113/jphysiol.2007.149989
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CELLULAR

Local calcium release activation by DHPR calcium channel openings in rat cardiac myocytes

 Eva Poláková1, Alexandra Zahradníková, Jr1, Jana Pavelková1, Ivan Zahradník1 and Alexandra Zahradníková1

1 Institute of Molecular Physiology and Genetics, Centre of Excellence for Cardiovascular Research, Slovak Academy of Sciences, Vlárska 5, 833 34 Bratislava, Slovakia

The principal role of calcium current in the triggering of calcium release in cardiac myocytes is well recognized. The mechanism of how calcium current (ICa) controls the intensity of calcium release is not clear because of the stochastic nature of voltage-dependent gating of calcium channels (DHPRs) and of calcium-dependent gating of ryanodine receptors (RyRs). To disclose the relation between DHPR openings and the probability of calcium release, local calcium release activation by ICa was investigated in rat ventricular myocytes using patch-clamp and confocal microscopy. Calcium spikes were activated by temporally synchronized DHPR calcium current triggers, generated by instantaneous ‘tail’ ICa and modulated by prepulse duration, by tail potential, and by the DHPR agonist BayK 8644. The DHPR–RyR coupling fidelity was determined from the temporal distribution of calcium spike latencies using a model based on exponentially distributed DHPR open times. The analysis provided a DHPR mean open time of ~0.5 ms, RyR activation time constant of ~0.6 ms, and RyR activation kinetics of the 4th order. The coupling fidelity was low due to the inherent prevalence of very short DHPR openings but was increased when DHPR openings were prolonged by BayK 8644. The probability of calcium release activation was high, despite low coupling fidelity, due to the activation of many DHPRs at individual release sites. We conclude that the control of calcium release intensity by physiological stimuli can be achieved by modulating the number and duration of DHPR openings at low coupling fidelity, thus avoiding the danger of inadvertently triggering calcium release events.

(Received 5 March 2008; accepted after revision 20 June 2008; first published online 26 June 2008)
Corresponding author A. Zahradníková: Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Vlárska 5, 833 34 Bratislava, Slovakia.  Email: alexandra.zahradnikova{at}savba.sk

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