Nitrovasodilators relax mesenteric microvessels by cGMP-induced stimulation of Ca-activated K channels

Abstract

Nitric oxide (NO) released from endothelial cells or exogenous nitrates is a potent dilator of arterial smooth muscle; however, the molecular mechanisms mediating relaxation to NO in the microcirculation have not been characterized. The present study investigated the relaxant effect of nitrovasodilators on microvessels obtained from the rat mesentery and also employed whole cell and single-channel patch-clamp techniques to identify the molecular target of NO action in myocytes from these vessels. Both sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP) relaxed phenylephrine-induced contractions by approximately 80% but were significantly less effective in relaxing contractions induced by 40 mM KCl. Relaxation to SNP was also inhibited by the K(+)-channel blocker tetraethylammonium or by inhibition of the activity of the guanosine 3',5'-cyclic monophosphate (cGMP)-dependent protein kinase (PKG). These results suggest that SNP stimulated K+ efflux by opening K+ channels via PKG-mediated phosphorylation. Perforated-patch experiments revealed that both SNP and SNAP increased outward currents in microvascular myocytes, and single-channel studies identified the high-conductance Ca(2+)- and voltage-activated K+ (BKCa) channel as the target of nitrovasodilator action. The effects of nitrovasodilators on BKCa channels were mimicked by cGMP and inhibited by blocking the activity of PKG. We conclude that stimulation of BKCa-channel activity via cGMP-dependent phosphorylation contributes to the vasodilatory effect of NO on microvessels and that a direct effect of NO on BKCa channels does not play a major role in this process. We propose that this mechanism is important for the therapeutic effect of nitrovasodilators on peripheral resistance and arterial blood pressure.

A cGMP-Dependent Protein Kinase Gene, foraging, Modifies Habituation-Like Response Decrement of the Giant Fiber Escape Circuit in Drosophila

“…This pleiotropy is paralleled at the cellular level in which these gene products have diverse molecular targets and actions. PKG serine/threonine kinases have numerous targets that could affect neuronal function and growth, such as ion channels (Stockand and Sansom 1996;Carrier et al 1997;Taguchi et al 1997;Alioua et al 1998;Han et al 1998;Vaandrager et al 1998;Wexler et al 1998), ATPases (e.g., Uneyama et al 1998), and regulators of gene expression (Gudi et al 1997;Idriss et al 1999). PKG may interact with other second messenger systems such as PKA, either by regulating such other systems (Moon et al 1998) or by phosphorylating common targets (Lengyel et al 1999).…”

Reconstitution of β-Adrenergic Modulation of Large Conductance, Calcium-activated Potassium (Maxi-K) Channels in Xenopus Oocytes

“…Considerable controversy exists with respect to the mechanism of stimulatory coupling to maxi-K channels. Stimulatory mechanisms that have been proposed include cAMP-dependent phosphorylation (5, 6, 11, 15, 16), cGMP-dependent phosphorylation (17,18,20,21,40), cGMP-dependent dephosphorylation (19,22,23), by G protein subunits (12,13), and direct stimulation by NO (41). We used the heterologous expression system and site-directed mutagenesis to identify the mechanism of ␤ adrenergic stimulatory coupling to maxi-K channels and to identify the relevant channel modulatory site.…”

N-Palmitoyl-ethanolamine (PEA) Induces Peripheral Antinociceptive Effect by ATP-Sensitive K+-Channel Activation

“…The molecular mechanism of this process begins with the activation of nitric oxide (NO) synthase, which produces the second messenger NO. NO then increases the intracellular level of cGMP, which can activate KATP (12,13). Based on experimental evidence that the peripheral antinociceptive effect of NO donors (14) and exogenous cGMP analogs (15) is mediated by KATP activation, it has been proposed that a link exists between the L-arginine/NO/cGMP pathway and KATP in the antinociceptive model (14,15).…”