Direct myocardial depressant effect of methylmethacrylate monomer: mechanical and electrophysiologic actions in vitro.
BACKGROUND
The present study explored the mechanism of direct myocardial depression by methylmethacrylate monomer (MMA).


METHODS
Isometric contraction of isolated guinea pig right ventricular papillary muscle was measured in modified normal and 26 mm K+ Tyrode solutions at various stimulation rates. Normal and slow action potentials were evaluated by conventional microelectrode technique. MMA effects on various aspects of sarcoplasmic reticulum function were evaluated by its effect on rapid-cooling contractures, rested-state contraction in rat papillary muscle in modified normal Tyrode solution, and in guinea pig papillary muscle under low Na+ (25 mm) Tyrode solution. Whole cell patch clamp techniques were applied to measure the inward Ca2+ currents (I(Ca)).


RESULTS
MMA (0.5, 1.5, and 4.7 mm) caused concentration-dependent depression of peak force and maximal rate of force development to approximately 70, 50, and 20% of baseline from rested state to 3 Hz stimulation rates, respectively. Depression of peak force and maximal rate of force development by MMA was dependent on stimulation frequency, with less depression at higher stimulation rates. In low Na+ Tyrode solution, 1.5 mm MMA depressed peak force of rat and guinea pig myocardium by 20-30%. In 26 mm K+ Tyrode solution, 0.5 and 1.5 mm MMA caused selective and marked concentration-dependent depression of late force development (0.5 mm: approximately 60% of baseline, 1.5 mm: approximately 30% of baseline) with no alteration in early force development. MMA (1.5 mm) depressed rapid-cooling contracture to 53 +/- 10% of baseline, accompanied by approximately 63% prolongation of time to peak contracture. In patch clamp studies, MMA reduced I(Ca) in a concentration-dependent manner.


CONCLUSIONS
The direct myocardial depressant effect of MMA seems to be caused in part by depression of Ca2+ influx through cardiac membrane, while depolarization-activated sarcoplasmic reticulum Ca2+ release appears modestly depressed.
Kim
Ki Jun
KJ
Department of Anesthesiology, Yonsei University College of Medicine, Seoul, South Korea.
Chen
Da Guang
DG
Chung
Namsik
N
Lynch
Carl
C
Park
Wyun Kon
WK
D000769:Anesthesia, Inhalation; D000818:Animals; D002118:Calcium / Q000502:physiology; D005260:Female; D006168:Guinea Pigs; D006221:Halothane; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D020366:Methylmethacrylate / Q000494:pharmacology*; D009200:Myocardial Contraction / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014665:Vasodilator Agents / Q000494:pharmacology
D014665:Vasodilator Agents; D020366:Methylmethacrylate; D002118:Calcium; D006221:Halothane