Abstract
This study examined the effect of 5 ns electric pulses on macroscopic ionic currents in whole-cell voltage-clamped adrenal chromaffin cells. Current-voltage (I-V) relationships first established that the early peak inward current was primarily composed of a fast voltage-dependent Na+ current (INa), whereas the late outward current was composed of at least three ionic currents: a voltage-gated Ca2+ current (ICa), a Ca2+-activated K+ current (IK(Ca)), and a sustained voltage-dependent delayed rectifier K+ current (IKV). A constant-voltage step protocol was next used to monitor peak inward and late outward currents before and after cell exposure to a 5 ns pulse. A single pulse applied at an electric (E)-field amplitude of 5 MV/m resulted in an instantaneous decrease of ~4% in peak INa that then declined exponentially to a level that was ~85% of the initial level after 10 min. Increasing the E-field amplitude to 8 or 10 MV/m caused a twofold greater inhibitory effect on peak INa. The decrease in INa was not due to a change in either the steady-state inactivation or activation of the Na+ channel but instead was associated with a decrease in maximal Na+ conductance. Late outward current was not affected by a pulse applied at 5 MV/m. However, for a pulse applied at the higher E-field amplitudes of 8 and 10 MV/m, late outward current in some cells underwent a progressive ~22% decline over the course of the first 20 s following pulse exposure, with no further decline. The effect was most likely concentrated on ICa and IK(Ca) as IKV was not affected. The results of this study indicate that in whole-cell patch clamped adrenal chromaffin cells, a 5 ns pulse differentially inhibits specific voltage-gated ionic currents in a manner that can be manipulated by tuning E-field amplitude.
Highlights
While the voltage-dependence and amplitude of the inward current remained stable over the course of 10 min or more, the outward current measured between 0 and +70 mV ran down in tens of seconds to a few minutes after seal rupture, which contrasted with outward currents elicited by moderate (e.g. –10 mV) and strong (e.g. +80 mV) depolarizations
The outward current at +40 mV is a mixture of a small voltage-dependent Ca2+ current, a large conductance Ca2+-activated K+ current (IK(Ca)), itself activated by Ca2+ entry through Ca2+ channels, and a sustained voltage-dependent delayed rectifier K+ current (IKV)
Since activation of IK(Ca) is triggered by ionic currents: a voltage-gated Ca2+ current (ICa), the rundown of the outward current observed between 0 and +70 mV would be consistent with the well-known rundown of several types of voltage-gated Ca2+ channels (e.g. L-type Ca2+ channels encoded by CaV1 subunits) [31,32,33] when recorded in the whole-cell patch clamp configuration [26,34]
Summary
Exposing biological cells to nanosecond-duration, high-intensity (>1 MV/m) electric pulses (NEPs) causes effects on the plasma membrane conductance properties of cells by forming. The very short duration of the pulses allows the electric field to penetrate the plasma membrane and cause intracellular effects, such as the release of calcium from internal stores [7,8,9] that can trigger various cell responses. The main effect of plasma membrane nanoporation is that of a cell stimulus to evoke catecholamine release When these cells are exposed to a single 5 ns, 5 MV/m pulse, voltage-gated Ca2+ channels (VGCCs) are activated, resulting in Ca2+ influx that triggers catecholamine release by exocytosis [19,20,21]. Na+ influx via plasma membrane nanopores could serve as an alternative depolarizing mechanism typically performed physiologically by activation of cation-permeable nicotinic receptors and subsequent stimulation of voltage-gated Na+ channels [23]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
