Effects of EMD 57033 on contraction and relaxation in isolated rabbit hearts.
BACKGROUND
Ca2+ sensitizers are reported to enhance contractility with modest effects on energy utilization. In the present study we assessed the effects of the relatively "pure" Ca2+ sensitizer EMD 57033 on mechanical performance and energy consumption in the beating heart.


RESULTS
In 10 isolated, red blood cell-perfused rabbit hearts the effects of EMD 57033 (5.0 to 5.8 mumol/L) on left ventricular (LV) pressure and O2 consumption (VO2) were examined at heart rates of 100 and 150 beats per minute (bpm) and perfusate [Ca2+] ([Ca2+]o) of 2.5 and 1.0 mmol/L (isovolumic contractions). LV developed pressure and maximum dP/dt increased, but less so at 150 bpm or 1.0 mmol/L [Ca2+]. End-diastolic pressure also increased, more so at 150 bpm or 1.0 mmol/L [Ca2+]o. EMD 57033 decreased time to peak isovolumic pressure (Tmax) and prolonged time to 50% pressure decline (T1/2). These changes were greater at slower heart rate or lower [Ca2+]o. The magnitude of increased VO2 with EMD 57033 was greater at 100 bpm than 150 bpm but unaffected by [Ca2+]o. We then investigated the influence of ejection on the response to EMD 57033 (n = 7). The increase in developed pressure with EMD 57033 was greater for ejecting than isovolumic beats (25.5 +/- 10.2 versus 14.7 +/- 7.5 mm Hg at 100 bpm, P < .01), while the increase in end-diastolic pressure was less (P = NS). The increase in VO2 was significantly greater for ejecting than isovolumic beats (0.027 +/- 0.013 versus 0.020 +/- 0.009 mL O2/beat per 100 g at 100 bpm, P < .01).


CONCLUSIONS
EMD 57033 enhances contractility and prolongs relaxation. Its effects are modulated by heart rate, [Ca2+]o, and contraction mode, with positive inotropic effects being more prominent for ejecting beats.
Hgashiyama
A
A
Cardiology Unit, College of Medicine, University of Vermont, Burlington, USA.
Watkins
M W
MW
Chen
Z
Z
LeWinter
M M
MM
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002316:Cardiotonic Agents / Q000494:pharmacology*; D002417:Cattle; D004734:Energy Metabolism / Q000187:drug effects; D004912:Erythrocytes; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D009206:Myocardium / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D010477:Perfusion; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D011804:Quinolines / Q000494:pharmacology*; D011817:Rabbits; D013829:Thiadiazines / Q000494:pharmacology*; D016277:Ventricular Function, Left / Q000187:drug effects; D017725:Ventricular Pressure / Q000187:drug effects
D002316:Cardiotonic Agents; D010726:Phosphodiesterase Inhibitors; D011804:Quinolines; D013829:Thiadiazines; C070609:EMD 53998; D002118:Calcium