Cell Stimulation and Calcium Mobilization by Picosecond Electric Pulses

We tested if picosecond electric pulses (psEP; 190 kV/cm, 500 ps at 50% height), which are much shorter than channel activation time, can activate voltage-gated (VG) channels. Cytosolic Ca2+ was monitored by Fura-2 ratiometric imaging in GH3 and NG108 cells (which express multiple types of VG calcium channels, VGCC), and in CHO cells (which express no VGCC). Trains of up to 100 psEP at 1 kHz elicited no response in CHO cells. However, even a single psEP significantly increased Ca2+ in both GH3 (by 114 +/- 48 nM) and NG108 cells (by 6 +/- 1.1 nM). Trains of 100 psEP amplified the response to 379 +/- 33 nM and 719 +/- 315 nM, respectively. Ca2+ responses peaked within 2-15 s and recovered for over 100 s; they were 80-100% inhibited by verapamil and omega-conotoxin, but not by the substitution of Na+ with N-methyl-D-glucamine. There was no response to psEP in Ca2+-free medium, but adding external Ca2+ even 10 s later evoked Ca2+ response. We conclude that electrical stimuli as short as 500 ps can cause long-lasting opening of VGCC by a mechanism which does not involve conventional electroporation, heating (which was under 0.06 K per psEP), or membrane depolarization by opening of VG Na+ channels