Local anesthetics modulate neuronal calcium signaling through multiple sites of action.
BACKGROUND
Local 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.


METHODS
Effects 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.


RESULTS
All 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.


CONCLUSIONS
Different 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.
Xu
Fang
F
Department of Anesthesiology, NYU Medical Center, 550 First Avenue, New York, New York 10016, USA. fang.xu@med.nyu.edu
Garavito-Aguilar
Zayra
Z
Recio-Pinto
Esperanza
E
Zhang
Jin
J
J  Blanck
Thomas J
TJ
D000577:Amides / Q000494:pharmacology; D000779:Anesthetics, Local / Q000494:pharmacology*; D020013:Calcium Signaling / Q000187:drug effects*; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D006801:Humans; D007700:Kinetics; D008012:Lidocaine / Q000494:pharmacology; D008619:Mepivacaine / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D011189:Potassium Chloride / Q000494:pharmacology; D000077212:Ropivacaine; D015222:Sodium Channels / Q000187:drug effects; D014407:Tumor Cells, Cultured
D000577:Amides; D000779:Anesthetics, Local; D015222:Sodium Channels; D011189:Potassium Chloride; D000077212:Ropivacaine; D002217:Carbachol; D008012:Lidocaine; D008619:Mepivacaine