Different Membrane Pathways Mediate Ca2+ Influx in Adrenal Chromaffin Cells Exposed to 150-400 ns Electric Pulses
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Exposing adrenal chromaffin cells to 5 ns electric pulses (nsPEF) causes a rapid rise in intracellular Ca2+ ([Ca2+] i) that is solely the result of Ca2+ influx through voltage-gated Ca2+ channels (VGCCs). This study explored the effect of longer duration nsPEF on [Ca2+] i. Single 150, 200, or 400 ns pulses at 3.1 kV/cm evoked rapid increases in [Ca2+] i, the magnitude of which increased linearly with pulse width and electric field amplitude. Recovery of [Ca2+] i to prestimulus levels was faster for 150 ns exposures. Regardless of pulse width, no rise in [Ca2+] i occurred in the absence of extracellular Ca2+, indicating that the source of Ca2+ was from outside the cell. Ca2+ responses evoked by a 150 ns pulse were inhibited to varying degrees by omega-agatoxin IVA, omega-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 Ca2+ influx insensitive to VGCC inhibitors was attributed to plasma membrane nanoporation, which comprised the E-field sensitive component of the response. Both pathways of Ca2+ entry were inhibited by 200 mu M Cd2+. These results demonstrate that, in excitable chromaffin cells, single 150-400 ns pulses increased the permeability of the plasma membrane to Ca2+ in addition to causing Ca2+ influx via VGCCs.