• Fang Xu, Zayra Garavito-Aguilar, Esperanza Recio-Pinto, Jin Zhang, and Thomas J J Blanck.
• Department of Anesthesiology, NYU Medical Center, 550 First Avenue, New York, New York 10016, USA. fang.xu@med.nyu.edu
• Anesthesiology. 2003 May 1;98(5):1139-46.

BackgroundLocal anesthetics (LAs) are known to inhibit voltage-dependent Na+ channels, as well as K+ and Ca2+ channels, but with lower potency. Since cellular excitability and responsiveness are largely determined by intracellular Ca2+ availability, sites along the Ca2+ signaling pathways may be targets of LAs. This study was aimed to investigate the LA effects on depolarization and receptor-mediated intracellular Ca2+ changes and to examine the role of Na+ and K+ channels in such functional responses.MethodsEffects of bupivacaine, ropivacaine, mepivacaine, and lidocaine (0.1-2.3 mm) on evoked [Ca2+](i) transients were investigated in neuronal SH-SY5Y cell suspensions using Fura-2 as the intracellular Ca2+ indicator. Potassium chloride (KCl, 100 mm) and carbachol (1 mm) were individually or sequentially applied to evoke increases in intracellular Ca2+. Coapplication of LA and Na+/K+ channel blockers was used to evaluate the role of Na+ and K+ channels in the LA effect on the evoked [Ca2+](i) transients.ResultsAll four LAs concentration-dependently inhibited both KCl- and carbachol-evoked [Ca2+](i) transients with the potency order bupivacaine > ropivacaine > lidocaine >/= mepivacaine. The carbachol-evoked [Ca2+](i) transients were more sensitive to LAs without than with a KCl prestimulation, whereas the LA-effect on the KCl-evoked [Ca2+](i) transients was not uniformly affected by a carbachol prestimulation. Na+ channel blockade did not alter the evoked [Ca2+](i) transients with or without a LA. In the absence of LA, K+ channel blockade increased the KCl-, but decreased the carbachol-evoked [Ca2+](i) transients. A coapplication of LA and K+ channel blocker resulted in larger inhibition of both KCl- and carbachol-evoked [Ca2+](i) transients than by LA alone.ConclusionsDifferent and overlapping sites of action of LAs are involved in inhibiting the KCl- and carbachol-evoked [Ca2+](i) transients, including voltage-dependent Ca2+ channels, a site associated with the caffeine-sensitive Ca2+ store and a possible site associated with the IP(3)-sensitive Ca2+ store, and a site in the muscarinic pathway. K+ channels, but not Na+ channels, seem to modulate the evoked [Ca2+](i) transients, as well as the LA-effects on such responses.

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