Intracellular [Ca(2+)] transients in Ca(2+) wave in single rat ventricular myocyte

Ca(2+) release from the sarcoplasmic reticulum (SR) in heart muscle grades depending on Ca(2+) influx in the physiological twitch; Ca(2+( wave results from regenerative Ca(2+) release from the SR. To examine if the Ca(2+) release from the SR in the Ca(2+) wave takes a duration similar to the physiological one, a transient rise of intracellular [Ca(2+)] ([Ca(2+)](i) transient) was recorded during both a propagating Ca(2+) wave and an electrically evoked twitch with single rat ventricular myocytes, using a laser scanning confocal microscope. Care was taken to record the fluo-3 fluorescence from a segmental region with little lateral movement, especially during a propagating Ca(2+) wave. During a typical Ca(2+) wave, the time-to-peak (TP) and the half-width (HD) of the averaged [Ca(2+)](i) transient were 161 and 253 ms respectively, but they were 76 and 145 ms during an electrically evoked twitch. The difference in the duration between the two types of [Ca(2+)](i) transients could not be accounted for by modification of duration of [Ca(2+)](i) transient by possible asynchronous Ca(2+) release from the SR during a Ca(2+) wave, suggesting that the regenerative Ca2+) release from the SR in the Ca2+) wave occurs more slowly than the physiological one in rat ventricular myocytes.