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(2+) ([Ca(2+)](i)) that is solely the result of Ca(2+) influx through voltage-gated Ca(2+) channels (VGCCs). This study explored the effect of longer duration nsPEF on [Ca(2+)](i). Single 150, 200, or 400 ns pulses at 3.1 kV/cm evoked rapid increases in [Ca(2+)](i), the magnitude of which increased linearly with pulse width and electric field amplitude. Recovery of [Ca(2+)](i) to prestimulus levels was faster for 150 ns exposures. Regardless of pulse width, no rise in [Ca(2+)](i) occurred in the absence of extracellular Ca(2+), indicating that the source of Ca(2+) was from outside the cell. Ca(2+) responses evoked by a 150 ns pulse were inhibited to varying degrees by ω-agatoxin IVA, ω-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(2+) influx insensitive to VGCC inhibitors was attributed to plasma membrane nanoporation, which comprised the E-field sensitive component of the response. Both pathways of Ca(2+) entry were inhibited by 200 μM Cd(2+). These results demonstrate that, in excitable chromaffin cells, single 150–400 ns pulses increased the permeability of the plasma membrane to Ca(2+) in addition to causing Ca(2+) influx via VGCCs.