Regulation of Intracellular Calcium by Bupivacaine Isomers in Cardiac Myocytes from Wistar Rats

In this study we investigated the effects of a racemic mixture of bupivacaine (RS(±)bupivacaine) and its isomers (S(-)bupivacaine and R(+)bupivacaine) on the Ca2+ handling by ventricular myocytes from Wistar rats. Single ventricular myocytes were enzymatically isolated and loaded with the fluorescent Ca2+ indicator fura 2-am to estimate intracellular Ca2+ concentration during contraction and relaxation cycles. S(-)bupivacaine (10 μM) significantly increased peak amplitude and the rate of increase of Ca2+ transients in 155% ± 54% (P < 0.05) and 194% ± 94% (P < 0.01) of control. However, exposure to R(+)bupivacaine had no effect on either peak amplitude or rate of increase at any concentration tested. Saponin-skinned ventricular fibers were used to investigate the effect of bupivacaine on the intracellular Ca2+ regulation by sarcoplasmic reticulum (SR) and on the Ca2+ sensitivity of contractile system. S(-), R(+), and RS(±)bupivacaine induced Ca2+ release from SR (P < 0.01). In SR-disrupted skinned ventricular cells, bupivacaine and its isomers (5 mM) increased the sensitivity of contractile system to Ca2+. S(-), RS(±), and R(+)bupivacaine significantly increased pCa50 from 5.8 ± 0.1, 5.8 ± 0.1, and 5.8 ± 0.1, to 6.1 ± 0.1 (P < 0.05), 6.0 ± 0.1 (P < 0.05), and 6.1 ± 0.1 (P < 0.05). Ca2+ release from SR through RyR2 activation could explain the increase of Ca2+ transients in cardiac cells. Increased intracellular Ca2+ in cardiac myocytes display a stereoselectivity to S(-)bupivacaine.