Comparison of the effects of mepivacaine and lidocaine on rat myocardium

BACKGROUND AND OBJECTIVE: To compare the inotropic and lusitropic effect of lidocaine and mepivacaine on rat papillary muscle. METHODS: Effects of lidocaine and mepivacaine (10-8-10-3 M) were studied in rat left ventricular papillary muscles in vitro at a calcium concentration of 1 mmol, under low (isotony) and high (isometric) loads. RESULTS: Lidocaine induced a significant negative inotropic effect in isotonic and isometric conditions whereas mepivacaine did not. Mepivacaine only induced a negative inotropic effect when added as a bolus for the highest concentration and this effect was significantly more pronounced with lidocaine than with mepivacaine (active force at 10-3 M: 63 +/- 10 vs. 84 +/- 10% of baseline, P < 0.05). Increasing calcium concentration resulted in a greater positive inotropic effect in the control (199 +/- 11% of baseline) and mepivacaine groups (197 +/- 22% of baseline) when compared to the lidocaine group (163 +/- 19% of baseline, P < 0.05 vs. lidocaine and control groups), suggesting an impairment on intracellular Ca2+ handling by lidocaine. A negative lusitropic effect under low load was observed only for mepivacaine and suggested an impairment of sarcoplasmic reticulum function. Lidocaine and mepivacaine did not modify post-rest potentiation but significantly depressed the force-frequency relationship. CONCLUSIONS: The negative inotropic and lusitropic effects induced by lidocaine were more important than that of mepivacaine and may involve an impairment of intracellular Ca2+ handling.