Nanosecond Electric Pulses: A Novel Stimulus for Triggering Ca Influx into Chromaffin Cells Via Voltage-Gated Ca Channels.

Exposing bovine chromaffin cells to a single 5 ns, high-voltage (5 MV/m) electric pulse stimulates Ca entry into the cells via L-type voltage-gated Ca channels (VGCC), resulting in the release of catecholamine. In this study, fluorescence imaging was used to monitor nanosecond pulse-induced effects on intracellular Ca level ([Ca]) to investigate the contribution of other types of VGCCs expressed in these cells in mediating Ca entry. ω-Conotoxin GVIA and ω-agatoxin IVA, antagonists of N-type and P/Q-type VGCCs, respectively, reduced the magnitude of the rise in [Ca] elicited by a 5 ns pulse. ω-conotoxin MVIIC, which blocks N- and P/Q-type VGCCs, had a similar effect. Blocking L-, N-, and P\Q-type channels simultaneously with a cocktail of VGCC inhibitors abolished the pulse-induced [Ca] response of the cells, suggesting Ca influx occurs only via VGCCs. Lowering extracellular K concentration from 5 to 2 mM or pulsing cells in Na-free medium suppressed the pulse-induced rise in [Ca] in the majority of cells. Thus, both membrane potential and Na entry appear to play a role in the mechanism by which nanoelectropulses evoke Ca influx. However, activation of voltage-gated Na channels (VGSC) is not involved since tetrodotoxin (TTX) failed to block the pulse-induced rise in [Ca]. These findings demonstrate that a single electric pulse of only 5 ns duration serves as a novel stimulus to open multiple types of VGCCs in chromaffin cells in a manner involving Na transport across the plasma membrane. Whether Na transport occurs via non-selective cation channels and/or through lipid nanopores remains to be determined. [ABSTRACT FROM AUTHOR]