Nanosecond electric pulse-induced calcium entry into chromaffin cells

Electrically excitable bovine adrenal chromaffin cells were exposed to nanosecond duration electric pulses at field intensities ranging from 2 MV/m to 8 MV/m and intracellular calcium levels ([Ca(2+)](i)) monitored in real time by fluorescence imaging of cells loaded with Calcium Green. A single 4 ns, 8 MV/m pulse produced a rapid, short-lived increase in [Ca(2+)](i), with the magnitude of the calcium response depending on the intensity of the electric field. Multiple pulses failed to produce a greater calcium response than a single pulse, and a short refractory period was required between pulses before another maximal increase in [Ca(2+)](i) could be triggered. The pulse-induced rise in [Ca(2+)](i) was not affected by depleting intracellular calcium stores with caffeine or thapsigargin but was completely prevented by the presence of EGTA, Co(2+), or the L-type calcium channel blocker nitrendipine in the extracellular medium. Thus, a single nanosecond pulse is sufficient to elicit a rise in [Ca(2+)](i) that involves entry of calcium via L-type calcium channels.