Different Membrane Pathways Mediate Ca2+ 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 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 onCa2+i. Single 150, 200, or 400 ns pulses at 3.1 kV/cm evoked rapid increases inCa2+i, the magnitude of which increased linearly with pulse width and electric field amplitude. Recovery ofCa2+ito prestimulus levels was faster for 150 ns exposures. Regardless of pulse width, no rise inCa2+ioccurred 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 byω-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 Ca2+influx insensitive to VGCC inhibitors was attributed to plasma membrane nanoporation, which comprised theE-field sensitive component of the response. Both pathways of Ca2+entry were inhibited by 200 μM 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.