In vitro effects of dantrolene on rat myocardium.
BACKGROUND
Dantrolene is the only known effective treatment for malignant hyperthermia. However, its effects on myocardial contraction and relaxation remain debatable.


METHODS
The effects of dantrolene (10(-5)-10(-3) M) on the contractility of rat left ventricular papillary muscles were investigated in vitro (Krebs-Henseleit solution, 29 degrees C, pH 7.40, 2.5 and 0.5 mM Ca2+, stimulation frequency 12 pulses/min). The authors studied contraction, relaxation, contraction-relaxation coupling under high and low load, energetics, and postrest potentiation. The effects of dantrolene after depletion of catecholamine stores with reserpine also were studied.


RESULTS
Dantrolene induced a moderate concentration-dependent negative inotropic effect at a low calcium concentration (active force at 10(-4) M: 86 +/- 14% of control values, P < 0.05), but not at a high calcium concentration. Dantrolene did not significantly modify the curvature of the force-velocity relation, suggesting that it did not modify myocardial energetics. Dantrolene induced no significant lusitropic effect under low load, suggesting that it did not modify calcium uptake by the sarcoplasmic reticulum. Dantrolene did not significantly modify postrest potentiation and postrest potentiation recovery, suggesting that it did not modify maximum capacity of calcium release by the sarcoplasmic reticulum nor its postrest resetting capacity. Reserpine did not modify the myocardial effects of dantrolene.


CONCLUSIONS
In rat myocardium, dantrolene did not modify any of the sarcoplasmic reticulum functions tested (uptake, release, postrest recovery). Dantrolene induced a moderate negative inotropic effect, probably mediated by a decrease in transarcolemmal calcium entry, and this negative inotropic effect was blunted by an increase in calcium concentration.
Fratea
S
S
Départment d'Anesthésie-Réanimation, Centre Hospitalo-universitaire (CHU) Pitié-Salpêtrière, Université Paris VI, France.
Langeron
O
O
Lecarpentier
Y
Y
Coriat
P
P
Riou
B
B
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D003620:Dantrolene / Q000494:pharmacology*; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D004734:Energy Metabolism / Q000187:drug effects; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D008297:Male; D009125:Muscle Relaxants, Central / Q000494:pharmacology*; D009126:Muscle Relaxation / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D010210:Papillary Muscles / Q000166:cytology; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000187:drug effects
D002121:Calcium Channel Blockers; D009125:Muscle Relaxants, Central; D003620:Dantrolene; D009543:Nifedipine; D002118:Calcium; D004121:Dimethyl Sulfoxide