[Autoregulation of the contractile function of the myocardium in response to changes in the concentration of the activating cation].
In guinea-pig isolated papillary muscles, dependence of the isotonic contraction velocity on the perfusate Ca++ concentration was studied. The dependence was the steepest at the lowest rate of stimulation. At a high rate (2 Hz), changes in contraction velocity as well as in extent of the muscle shortening were minimal. Replacement of a half of Ca++ ions by Sr++ resulted in an augmentation of steepness of the dependence on sum of [Ca++] and [Sp++], and in a more prominent fall in relaxation velocity as compared with contraction velocity. Replacement of a half of Ca++ ions with Ba++ or depletion of [Na+] in usual solution to 25 mM resulted in a prominent fall in relaxation velocity while the contraction velocity increased. This dissociation coincided with signs of cellular Ca++ overload and a more steep restitution of contraction velocity during diastole. Results are discussed in terms of participation of Na+-Ca++ exchange in these self-regulatory phenomena.
V I
VI
Kapel'ko
M S
MS
Gorina
D000818:Animals; D001464:Barium / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology*; D004558:Electric Stimulation; D006168:Guinea Pigs; D007036:Hypothermia, Induced; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects*; D010210:Papillary Muscles / Q000187:drug effects; D012964:Sodium / Q000494:pharmacology*; D013324:Strontium / Q000494:pharmacology*
D001464:Barium; D012964:Sodium; D002118:Calcium; D013324:Strontium
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