Intracellular Calcium Increases in Growth Cones Exposed to Tetracaine

Perturbation of Ca2+ stores and store-operated Ca2+ influx by lidocaine in neuronal N2A and NG108-15 cells

In this report we examined the effects of lidocaine on Ca²⁺ homeostasis of neuronal cells using microfluorimetric measurement of cytosolic Ca²⁺ with fura 2 as probe. In mouse neuroblastoma N2A cells, 10 mM lidocaine caused Ca²⁺ release from the cyclopiazonic acid (CPA)-dischargeable pool and abolished ATP-triggered Ca²⁺ release. Lidocaine-triggered Ca²⁺ release was not affected by xestospongin C (XeC), an inositol 1,4,5-trisphosphate receptor (IP3R) inhibitor. N2A cells did not have functional ryanodine receptors (RYR) (absence of caffeine response) and we used differentiated NG108-15 cells (presence of caffeine response) for further experiments. Caffeine-triggered Ca²⁺ release was unaffected by a brief lidocaine exposure, but was eliminated after a prolonged treatment of lidocaine, suggesting lidocaine abolished caffeine action possibly not by interfering caffeine binding but via Ca²⁺ store depletion. Lidocaine-elicited Ca²⁺ release was unaffected by XeC or a high concentration of ryanodine, suggesting Ca²⁺ release was not via IP3R or RYR. Lidocaine did not affect nigericin-dischargeable lysosomal Ca²⁺ stores. Lastly, we observed that lidocaine suppressed CPA-induced store-operated Ca²⁺ influx in both N2A cells and differentiated NG108-15 cells. Our results suggest two novel actions of lidocaine in neuronal cells, namely, depletion of Ca²⁺ store (via an IP3R- and RYR-independent manner) and suppression of store-operated Ca²⁺ influx.

Local anesthetic toxicity: acute and chronic management

Local anesthetics are commonly used medicines in clinical settings. They are used for pain management during minor interventional treatments, and for postoperative care after major surgeries. Cocaine is the well‐known origin of local anesthetics, and the drug and related derivatives have long history of clinical usage for more than several centuries. Although illegal use of cocaine and its abuse are social problem in some countries, other local anesthetics are safely and effectively used in clinics and hospitals all over the world. However, still this drug category has several side‐effects and possibilities of rare but serious complications. Acute neurotoxicity and cardiac toxicity are derived from unexpected high serum concentration. Allergic reactions are observed in some cases, especially following the use of ester structure drugs. Chronic toxicity is provoked when nerve fibers are exposed to local anesthetics at a high concentration for a long duration. Adequate treatments for acute toxic reactions can secure complete recovery of patients, and careful use of drugs prevents long‐lasting neurological complications. In addition to respiratory and circulatory management, effectiveness of lipid rescue in the acute toxicity treatment has been certified in many clinical guidelines. Prevention of the use of high concentration of local anesthetics is also validated to be effective to decrease the possibility of nerve fiber damage.

Inhibitory gene expression of the Cav3.1 T-type calcium channel to improve neuronal injury induced by lidocaine hydrochloride

Cav3.1 is a low-voltage-activated (LVA) calcium channel that plays a key role in regulating intracellular calcium ion levels. In this study, we observed the effects of lidocaine hydrochloride on the pshRNA-CACNA1G-SH-SY5Y cells that silenced Cav3.1 mRNA by RNA interference, and investigated the roles of p38 MAPK in these effects. We constructed the pNC-puro-CACNA1G-SH-SY5Y cells and pshRNA-CACNA1G -SH-SY5Y cells by the RNA interference. All the cells were cultured with or without 10mM lidocaine hydrochloride for 24 h. The cell morphology, cell viability, Cav3.1 and p38 protein expression, cell apoptosis rate and intracellular calcium ion concentration were detected. We found that all cells treated with 10mM lidocaine hydrochloride for 24 h showed cellular rounding, axonal regression, and cellular floating. Compared with the cells in SH-SY5Y+Lido group and NC+Lido group, those in the RNAi+Lido group showed similar changes, but of smaller magnitude. Additionally, following lidocaine hydrochloride all cells displayed increased Cav3.1 and p38 MAPK protein, apoptosis rate, and intracellular calcium ion levels; however,these changes in the RNAi+Lido group were less pronounced than in the SH-SY5Y+Lido and NC+Lido groups. The cell viability decreased following lidocaine hydrochloride treatment, but viability of the cells in the RNAi+Lido group was higher than in the SH-SY5Y+Lido and NC+Lido groups. The results showed that Cav3.1 may be involved in neuronal injury induced by lidocaine hydrochloride and that p38 MAPK phosphorylation was reduced upon Cav3.1 gene silencing.

Tetracaine at a small concentration delayed nerve growth without destroying neurites and growth cones

Local anesthetics have direct neurotoxicity and induce growth cone collapse when applied to neurons at large concentrations. However, the effects of prolonged exposure to local anesthetics at a small concentration have never been studied. We examined whether neurite growth was slowed by tetracaine at small concentrations in chick embryo dorsal root ganglions. The effects of tetracaine were examined microscopically and by a neurite growth rate assay, quantitative morphologic assay, growth cone collapse assay, and Western blot assay. Neurite growth 24 and 48 h after application was delayed significantly when tetracaine was applied at a concentration larger than 5 microM. Filopodia of growth cones retracted, and their number was significantly decreased 24 and 48 h after the application of 10 and 20 microM of tetracaine. The quantity of actin in cell bodies increased, contrary to the effect on neurites and growth cones, where actin decreased 48 h after the application of 5, 10, and 20 microM of tetracaine. In conclusion, continuous exposure to tetracaine at small concentrations delayed neurite growth, reduced the number of filopodia, and decreased actin content.

Increase in intracellular Ca2+ concentration is not the only cause of lidocaine-induced cell damage in the cultured neurons of Lymnaea stagnalis

PURPOSE

To determine whether the increase in intracellular Ca2+ concentration induced by lidocaine produces neurotoxicity, we compared morphological changes and Ca2+ concentrations, using fura-2 imaging, in the cultured neurons of Lymnaea stagnalis.

METHODS

We used BAPTA-AM, a Ca2+ chelator, to prevent the increase in the intracellular Ca2+ concentration, and Calcimycin A23187, a Ca2+ ionophore, to identify the relationship between increased intracellular Ca(2+) concentrations and neuronal damage without lidocaine. Morphological changes were confirmed using trypan blue to stain the cells.

RESULTS

Increasing the dose of lidocaine increased the intracellular Ca2+ concentration; however, there was no morphological damage to the cells in lidocaine at 3 x 10(-3) M. Lidocaine at 3 x 10(-2) M increased the intracellular Ca2+ concentration in both saline (from 238 +/- 63 to 1038 +/- 156 nM) and Ca2+-free medium (from 211 +/- 97 to 1046 +/- 169 nM) and produced morphological damage and shrinkage, with the formation of a rugged surface. With the addition of BAPTA-AM, lidocaine at 3 x 10(-2) M moderately increased the intracellular Ca2+ concentration (from 150 +/- 97 to 428 +/- 246 nM) and produced morphological damage. These morphologically changed cells were stained dark blue with trypan blue dye. The Ca2+ ionophore increased the intracellular Ca2+ concentration (from 277 +/- 191 to 1323 +/- 67 nM) and decreased it to 186 +/- 109 nM at 60 min. Morphological damage was not observed during the 60 min, but became apparent a few hours later.

CONCLUSION

These results indicated that the increase in intracellular Ca2+ concentration is not the only cause of lidocaine-induced cell damage.