A-type K+ channels contribute to the prorenin increase of firing activity in hypothalamic vasopressin neurosecretory neurons

Recent studies have supported an important contribution of prorenin (PR) and its receptor (PRR) to the regulation of hypothalamic, sympathetic, and neurosecretory outflows to the cardiovascular system, including systemic release of vasopressin (VP), both under physiological and cardiovascular disease conditions. Still, the identification of precise cellular mechanisms and neuronal/molecular targets remain unknown. We have recently shown that PRR is expressed in VP neurons and that their activation increases neuronal activity. However, the underlying ionic channel mechanisms are undefined. Here, we performed patch-clamp electrophysiology from identified VP neurons in acute hypothalamic slices obtained from enhanced green fluorescent protein-VP transgenic rats. Voltage-clamp recordings showed that PR inhibited the magnitude of A-type K+ current (IA; ~50% at –25 mV), a subthreshold voltage-dependent current that restrains VP firing activity. PR also increased the inactivation rate of IA and shifted the steady-state voltage-dependent inactivation function toward more hyperpolarized membrane potential (~7 mV shift), thus resulting in less channel availability to be activated at any given membrane potential. PR also inhibited a sustained component of IA ("window" current). PR-mediated changes in action potential waveform and increased firing activity were occluded when IA was blocked by 4-aminopyridine. Finally, PR failed to increase superoxide production within the supraopti...
Source: AJP: Heart and Circulatory Physiology - Category: Cardiology Authors: Tags: RESEARCH ARTICLE Source Type: research