Two subtypes of dihydropyridine-sensitive calcium channels in rat ventricular muscle.
Two opposite inotropic effects of the dihydropyridine activators, CGP 28392 and Bay K 8644, given at the same concentration (1-2 microM) were found in rat papillary muscles: a positive effect in polarized tissue (4 mM KCl) and a negative one during partial depolarization. The depressive effect found at a low rate or after a short rest was associated with marked prolongation of the Ca2(+)-mediated action potential, indicating that the drugs behave as Ca channel stimulators. The depressive effect of the activation on the resting state contraction was antagonized by nifedipine (2 microM) and high Mg2+ (5 mM). It was suggested that at least two subtypes of the L-type, dihydropyridine-sensitive channels underlie the opposite inotropic responses of the activators. The positive effect is apparently caused by conventional stimulation of Ca2+ entry through the cell membrane, whereas the negative effect is probably due to the stimulation of Ca2+ efflux from the sarcoplasmic reticulum, leading to depletion of intracellular stores. The effect was proposed to be mediated by activation of junctional channels linked to sarcoplasmic reticulum Ca2+ release. An important role for these channels in triggering the sarcoplasmic reticulum Ca2+ release and regulation of force-frequency relation is proposed.
Saxon
M
M
Institute of Biological Physics, Academy of Sciences of the U.S.S.R., Pushchino, Moscow.
Gainullin
R
R
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D004095:Dihydropyridines / Q000494:pharmacology*; D005260:Female; D006321:Heart / Q000187:drug effects; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism
D002120:Calcium Channel Agonists; D015220:Calcium Channels; D004095:Dihydropyridines; D011725:Pyridines; D011189:Potassium Chloride; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C040525:CGP 28392; D008274:Magnesium; D009543:Nifedipine