Roles of intracellular Ca^<2+> in genesis of life-threatening arrhythmia.

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Cytosolic Calcium Stairacase in Ventricular Myocytes Isolated from Guinea-pigs and Psts. Dynamic changes in cytosolic calcium concenyration ([Ca^<2+>]) in single myocytes were investigated using a ca^<2+> sensitive fluorescence dye, fura2, to elucidate the mechanism of the tension staircase phenomenon of mammalian hearts. A stimulation train at 1.0 H_z after a 3 min rest period produced an ascending staircase of (Ca^<2+>]i transients in guinea-pig myocytes, while a descending staircase of [Ca^<2+>]i transients in rat myocytes. During the same stimulation protocol, an inhibitor of the sarcoplasmic reticulum (the SR), ryanodine (1 uM), sigh, ficantly depressed the leve of [Ca^<2+>]i in rat myocytes, while did not appreciably affected [Ca^<2+>]i transients in guinea-pig myocytes. These results suggested that in rat myocytes the SR plays important role in the genesis of the negative contractile staircase phenomenon, while in guinea-pig myocytes the Ca^<2+> movement across the salcolemma is … More important for the genesis of the positive contractile staircase phenomenon.Flutuation of Cytosolic Calcium Concentration ([Ca^<2+>]i) Following Resumption of Oxidative phosphorylation in Single Guinea-pig Myocytes.Dynamics of [Ca^<2+>]i transients following resumption of oxidative phosphorylation were examined in single guinea-pig myocytes using a Ca^<2+>-sensitive fluorescent dye, fura2, in order to elucidate mechanisms of the reperfusion arrhythmia. Resumption of oxidative phosphorylation, produced by a wash-out after 5-min exposure to DNP(0.1 mM), caused a significant rise of both systolic and diastolic [Ca^<2+>]i associated with spatially and gemetrically inhomogenous fluctuations of [Ca^<2+>]i, which were accompanied by the spontaneous contractile wave and fluctuation of the membrane potential. An addition of ryanodine(1uM) to the wash-out solution, almost completely abolished the occurrence of both the [Ca^<2+>]i and membrane potential fluctuations. These results suggest that the Ca^<2+> release from the sarcoplasmic reticulum is involved in the fluctuation of [Ca^<2+>]i and membrane potential that occurs following resumption of oxdative phosphorylation. Less