[Role of sarcoplasmic reticulum in the regulation of myocardial relaxation].
In order to investigate cardiac muscle behavior after inhibition of either sarcoplasmic reticulum (SR) Ca2+ release or SR Ca2+ uptake, 35 papillary muscles of adult Wistar rats were studied after a 60 minutes exposure to ryanodine 10(-7) M (n = 11) or to cyclopiazonic acid (CPA) 10(-5) M (n = 14) and compared with a control group containing the solvent alone (n = 10). We measured the maximum extent of muscle shortening of the preloaded twitch (DLp) and the normalized total force of the fully isometric twitch (FTi). The peak lengthening velocity of the preloaded twitch (VRp) and the normalized negative peak force derivative of the fully isometric twitch (-DFi) tested the lusitropic state. Intrinsic changes in the relaxation phase, independent of the contractile state, i.e., the relaxant effects, were analysed using 1) two ratios; the VRp/DLp ratio of the preloaded twitch and the -DFi/FTi ratio of the fully isometric twitch and 2) the slopes of the VR versus DL and of the -DF versus FT relationship over the whole continuum of load. Ryanodine induced a marked negative inotropic effect associated with a decrease in VRp from 2.7 +/- 0.2 to 1.4 +/- 0.2 Lmax/s (p < 0.001). The VRp/DLp ratio and the slope of the VR versus DL relationship remained unchanged, indicating that ryanodine was devoid of intrinsic relaxant effect under isotonic conditions. At a 10/min stimulation frequency, inhibition of Ca(2+)-uptake function of the SR with CPA had no inotropic effect but decreased VRp from 2.9 +/- 0.1 to 2.2 +/- 0.1 Lmax/s (p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
INSERM U 275-LOA-ENSTA-Ecole Polytechnique, Palaiseau.
N
N
Péry-Man
D
D
Chemla
C
C
Coirault
I
I
Suard
Y
Y
Lecarpentier
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects; D003971:Diastole / Q000187:drug effects / Q000502:physiology; D007211:Indoles / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D010210:Papillary Muscles / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000502:physiology*
D015220:Calcium Channels; D007211:Indoles; D012433:Ryanodine; C000543:cyclopiazonic acid
Rôle du réticulum sarcoplasmique dans la régulation de la relaxation myocardique.