Tight coupling between the rate of rise of Ca2+ transient and peak twitch contraction in guinea-pig papillary muscle.
We evaluated the relationship between cytoplasmic Ca2+ concentration ([Ca2+]i) and force in guinea-pig papillary muscles loaded with a fluorescent Ca2+ indicator, fura-PE3. In the absence of ryanodine, [Ca2+]i transient and force were altered by changing extracellular Ca2+ concentration and stimulation frequency, and also by adding methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyri dine-5-carboxylate (Bay K 8644) or ouabain. Under these conditions, the peak force correlated linearly with the maximal rate of rise of [Ca2+]i (gamma = 0.948) more than the peak [Ca2+]i transient (gamma = 0.737). Ryanodine inhibited the increase in the maximal rate of rise of [Ca2+]i resulting in abolishment of the correlation between force and the maximal rate of rise of [Ca2+]i. These results suggest that the maximal rate of rise of [Ca2+]i reflects Ca2+ release from the sarcoplasmic reticulum, and this fraction of [Ca2+]i is crucial for determining the amplitude of twitch contractions when the sarcoplasmic reticulum is intact in guinea-pig papillary muscle.
Miyamoto
S
S
Department of Veterinary Pharmacology, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Japan. aa57142@hongo.ecc.u-tokyo.ac.jp
Ozaki
H
H
Hori
M
M
Endoh
M
M
Karaki
H
H
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D002316:Cardiotonic Agents / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005456:Fluorescent Dyes / Q000032:analysis; D016257:Fura-2 / Q000031:analogs & derivatives / Q000032:analysis; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D010042:Ouabain / Q000494:pharmacology; D010210:Papillary Muscles / Q000187:drug effects*; D012433:Ryanodine / Q000494:pharmacology; D013997:Time Factors
D002316:Cardiotonic Agents; D005456:Fluorescent Dyes; C098106:fura-PE3; D012433:Ryanodine; D010042:Ouabain; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D002118:Calcium; D016257:Fura-2