Endothelium-derived hyperpolarizing factor (EDHF) in rat mesenteric artery.

Abstract

The endothelium, a critical modulator of vascular resistance and blood pressure, can release at least three factors that relax vascular smooth muscle, including nitric oxide (NO), prostacyclin (prostaglandin I2, PGI 2), and endothelium-derived hyperpolarizing factor (EDHF). EDHF-induced relaxation is correlated with a strong hyperpolarization and may activate vascular smooth muscle cell (VSMC) K-channels. The research presented studied ACh-induced EDHF release from rat tail artery (TA) and superior mesenteric artery (SMA). Calcium-activated potassium (KCa) channels in the rat mesenteric resistance artery (MRA), putative targets of EDHF, were characterized. ACh-induced EDHF release from rat TA or SMA hyperpolarized target single TA VSMCs current-clamped with the nystatin perforated patch technique. In the absence of donor tissue, ACh induced depolarization. TA and MRA VSMCs were patch clamped in the whole-cell configuration and macroscopic K-currents were elicited by depolarizing pulses. Calcium-activated (KCa) and voltage-dependent (Kdr) potassium currents were observed in both TA and MRA VSMCs. Apamin (300 nM) significantly inhibited MRA (79% of control at +50 mV) but not TA whole-cell KCa Current. Iberiotoxin (IbTX) or charybdotoxin (ChTX) (150 nM) abolished KCa current in TA and MRA VSMCs. Single rat MRA VSMCs were patch clamped using the inside-out technique. Four KCa channels were observed and named: BK. IK, SK, and miniK (big, intermediate, small, and mini KCa channels). In symmetrical potassium (150 mM), the single channel conductances were linear (BK, 197: IK, 94; SK, 50; miniK, 31 pS) and similar to those observed in rat TA. ChTX (150 nM) completely blocked the BK, IK, and miniK channels, and dramatically inhibited the SK channel (inside-out. +40 mV, [Ca2+] i = 500 nM). IbTX (150 nM) completely blocked all MRA KCa channels. 4-AP (2 mM) completely blocked the BK and IK channels, partially blocked the SK channel, and dramatically inhibited the miniK channel. Apamin (300 nM) selectively blocked the BK channel. (Abstract shortened by UMI.)