Analysis of the staircase phenomenon of the cardiac muscle contraction under the patch clamp conditions

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Under the patch clamp conditions, we recorded changes in the sarcomere pattern by projecting the image of the single ventricular myocyte onto the linear image sensor in parallel to the membrane current recordings. The cycle length of individual sarcomere, when recorded every 2 msec, showed a micro fluctuations even under the holding potential at -40 mV. When the external Ca^<2+> is removed, the fluctuation was largely depressed. Under the Ca^<2+> overload conditions, induced by applying 5.4 mM Ca^<2+> and ouabain, the miniature fluctuations were largely enhanced as revealed by the increase in the power below 10 Hz in the FFT analysis. The application of ryanodine suppressed these fluctuations, leaving the mean sarcomere length relatively short. When the cell contraction was evoked by applying depolarizing pulses, the variation among different sarcomeres within the cell was increased when compared with the resting condition. This was typically observed when the open probability of the L-type Ca^<2+> channels was low at the test pulse to -30 mV. These findings well supported the local control theory of the excitation-contraction coupling.