Ryanodine Does Not Produce Negative Chronotropic Effect on Action Potential Generation in Heart Pacemaker Cells of Young Frogs Rana temporaria

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The goal of the present work consisted in studying role of Ca2+ released via ryanodine-sensitive receptors of the sarcoplasmic reticulum in modulation of frequency of action potential (AP) generation of cells of the pacemaker type of the young and adult frog heart. Ryanodine (3 μM) decreased the AP generation frequency in adult frogs by 43%, while produced no effect in young animals. Duration of the diastolic depolarization decreased more than twice as compared with control. Ryanodine (20 μM) inhibited completely the AP generation spontaneous activity in adult frogs, whereas in young animals the negative chronotropic effect was observed, on average, by 14%. The rate of diastolic depolarization did not change. Based on analysis of our obtained data and the literature data, we have concluded that in young frogs there takes place the spatial-temporal uncoupling of the sarcoplasmic reticulum and the sarcolemmal membrane.

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