Mepivacaine reduces calcium transients in isolated murine ventricular cardiomyocytes

BACKGROUND: The potential mechanism of mepivacaine’s myocardial depressant effect observed in papillary muscle has not yet been investigated at cellular level. Therefore, we evaluated mepivacaine’s effects on Ca(2+) transient in isolated adult mouse cardiomyocytes. METHODS: Single ventricular myocytes were enzymatically isolated from wild-type C57Bl/6 mice and loaded with 10 μM fluorescent Ca(2+) indicator Fluo-4-AM to record intracellular Ca(2+) transients upon electrical stimulation. The mepivacaine effects at half-maximal inhibitory concentration (IC(50)) was determined on calibrated cardiomyocytes’ Ca(2+) transients by non-parametric statistical analyses on biophysical parameters. Combination of mepivacaine with NCX blockers ORM-10103 or NiCl(2) were used to test a possible mechanism to explain mepivacaine-induced Ca(2+) transients’ reduction. RESULTS: A significant inhibition at mepivacaine’s IC(50) (50 μM) on Ca(2+) transients was measured in biophysical parameters such as peak (control: 528.6 ± 73.61 nM vs mepivacaine: 130.9 ± 15.63 nM; p < 0.05), peak area (control: 401.7 ± 63.09 nM*s vs mepivacaine: 72.14 ± 10.46 nM*s; p < 0.05), slope (control: 7699 ± 1110 nM/s vs mepivacaine: 1686 ± 226.6 nM/s; p < 0.05), time to peak (control: 107.9 ± 8.967 ms vs mepivacaine: 83.61 ± 7.650 ms; p < 0.05) and D(50) (control: 457.1 ± 47.16 ms vs mepivacaine: 284.5 ± 22.71 ms; p < 0.05). Combination of mepivacaine with NCX blockers ORM-10103 or NiCl(2) showed a significant increase in the baseline of [Ca(2+)] and arrhythmic activity upon electrical stimulation. CONCLUSION: At cellular level, mepivacaine blocks Na(+) channels, enhancing the reverse mode activity of NCX, leading to a significant reduction of Ca(2+) transients. These results suggest a new mechanism for the mepivacaine-reduction contractility effect.