Different Membrane Pathways Mediate Ca 2+ Influx in Adrenal Chromaffin Cells Exposed to 150-400 ns Electric Pulses

Exposing adrenal chromaffin cells to 5 ns electric pulses (nsPEF) causes a rapid rise in intracellular Ca ([Ca ] ) that is solely the result of Ca influx through voltage-gated Ca channels (VGCCs). This study explored the effect of longer duration nsPEF on [Ca ] . Single 150, 200, or 400 ns pulses at 3.1 kV/cm evoked rapid increases in [Ca ] , the magnitude of which increased linearly with pulse width and electric field amplitude. Recovery of [Ca ] to prestimulus levels was faster for 150 ns exposures. Regardless of pulse width, no rise in [Ca ] occurred in the absence of extracellular Ca , indicating that the source of Ca was from outside the cell. Ca responses evoked by a 150 ns pulse were inhibited to varying degrees by -agatoxin IVA, -conotoxin GVIA, nitrendipine or nimodipine, antagonists of P/Q-, N-, and L-type VGCCs, respectively, and by 67% when all four types of VGCCs were blocked simultaneously. The remaining Ca influx insensitive to VGCC inhibitors was attributed to plasma membrane nanoporation, which comprised the -field sensitive component of the response. Both pathways of Ca entry were inhibited by 200 M Cd . These results demonstrate that, in excitable chromaffin cells, single 150-400 ns pulses increased the permeability of the plasma membrane to Ca in addition to causing Ca influx via VGCCs.