Action potential duration and force-frequency relationship in isolated rabbit, guinea pig and rat cardiac muscle.
The effect of action potential duration and elevated cytosolic sodium concentration on the force-frequency relationship in isolated rabbit, guinea pig and rat papillary muscle preparations was studied. Shortening of action potential duration in guinea pig and rabbit from 150-200 ms to values characteristic of rat (20-40 ms), using the K(ATP) channel activator levkromakalim (15 mumol.l-1), markedly reduced the force of contraction and converted the positive force-frequency relationship into negative one at longer pacing cycle lengths. This conversion was greatly enhanced in the presence of acetylstrophanthidin (0.2-1 mumol.l-1), an inhibitor of the Na-K pump. Acetylstrophanthidin (1 mumol.l-1) alone, however, had no effect on the force-frequency relationship. Prolongation of action potential duration in rat with inhibitors of cardiac K channels (4-aminopyridine [10 mmol.l-1] plus tetraethylammonium [2 mmol.l-1) increased the force of contraction and abolished the negative force-frequency relationship observed in rat at longer pacing-cycle lengths. It is concluded that both action potential duration and cytosolic sodium concentration are major determinants of the force-frequency relationship in mammalian myocardium.
Szigligeti
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P
Department of Physiology, University Medical School of Debrecen, Hungary.
Pankucsi
C
C
Bányász
T
T
Varró
A
A
Nánási
P P
PP
D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001578:Benzopyrans / Q000494:pharmacology; D019806:Cromakalim; D003600:Cytosol / Q000378:metabolism; D006146:Guanidines / Q000494:pharmacology; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000502:physiology*; D020110:Pinacidil; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D011758:Pyrroles / Q000494:pharmacology; D011817:Rabbits; D051381:Rats; D012964:Sodium / Q000378:metabolism; D013327:Strophanthidin / Q000031:analogs & derivatives / Q000494:pharmacology; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D001578:Benzopyrans; D006146:Guanidines; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D011758:Pyrroles; D013757:Tetraethylammonium Compounds; D019806:Cromakalim; D013327:Strophanthidin; D019789:Tetraethylammonium; D020110:Pinacidil; D012964:Sodium; D015761:4-Aminopyridine; C004681:acetylstrophanthidin