Modulation of intracellular Ca2+ levels in chromaffin cells by nanoelectropulses

Exposing chromaffin cells to a single 5 ns, 5 MV/m pulse causes Ca2+ influx and a rapid, transient rise in intracellular calcium concentration ([Ca2+](i)). A comparison of responses at room temperature versus 37 degrees C revealed no effect of temperature on the magnitude of the increase in [Ca2+](i). The Ca2+ transient, however, was shortened in duration almost twofold at 37 degrees C, indicating that the rate of recovery was temperature-sensitive. Temperature also affected the interval required for a second pulse to elicit another maximal rise in [Ca2+](i), which was shorter at the higher temperature. In addition, a second pulse applied 5 s after the first pulse was sufficient to cause cells at room temperature to become refractory to subsequent stimulation. At 37 degrees C, cells became refractory after 5 pulses regardless of whether pulse delivery was at low (1 and 10 Hz) or high (1 kHz) rates. When refractory, cells showed no signs of swelling or uptake of the impermeant dye YO-PRO-1. These results demonstrate that temperature plays a role in determining how chromaffin cells respond to and become refractory to nanoelectropulses. They also indicate that despite the ultra-short duration of the pulses, pronounced effects on cell excitability result from the application of only very few pulses. (C) 2011 Elsevier B.V. All rights reserved.