Effects of levobupivacaine and bupivacaine on intracellular calcium signaling in cultured rat dorsal root ganglion neurons.

Bupivacaine and levobupivacaine have been shown to be effective in the treatment of pain as local anesthetics, although the mechanisms mediating their antinociceptive actions are still not well understood. The aim of this study was to investigate the effects of bupivacaine and levobupivacaine on intracellular calcium ([Ca(2+)](i)) signaling in cultured rat dorsal root ganglion (DRG) neurons. DRG neuronal cultures loaded with 5 microM Fura-2/AM and [Ca(2+)](i) transients for stimulation with 30 mM KCl (Hi K(+)) were assessed by using fluorescent ratiometry. DRGs were excited at 340 and 380 nm, emission was recorded at 510 nm, and responses were determined from the change in the 340/380 ratio (basal-peak) for individual DRG neurons. Data were analyzed by using Student's t-test. Levobupivacaine and bupivacaine attenuated the KCl-evoked [Ca(2+)](i) transients in a reversible manner. [Ca(2+)](i) increase evoked by Hi K(+) was significantly reduced to 99.9 +/- 5.1% (n = 18) and 62.5 +/- 4.2% (n = 15, P < 0.05) after the application of 5 and 50 microM levobupivacaine, respectively. Bupivacaine also inhibited Hi K(+)-induced [Ca(2+)](i) responses, reduced to 98.7 +/- 4.8% (n = 10) and 69.5 +/- 4.5% (n = 9, P < 0.05) inhibition of fluorescence ratio values of Hi K(+)-induced responses at 5 and 50 microM, respectively. Our results indicate that bupivacaine and levobupivacaine, with no significant differences between both agents, attenuated KCl-evoked calcium transients in a reversible manner. The inhibition of calcium signals in DRG neurons by levobupivacaine and bupivacaine might contribute to the antinociceptive effects of these local anesthetics.