Nitric oxide (NO)‐induced activation of large conductance Ca²⁺‐dependent K⁺ channels (BK_Ca) in smooth muscle cells isolated from the rat mesenteric artery

Abstract

1 To assess the action of nitric oxide (NO) and NO-donors on K + current evoked either by voltage ramps or steps, patch clamp recordings were made from smooth muscle cells freshly isolated from secondary and tertiary branches of the rat mesenteric artery. 2 Inside-out patches contained channels, the open probability of which increased with [Ca 2+ ] i . The channels had a linear slope conductance of 212+5 pS (n=12) in symmetrical (140 mM) K + solutions which reversed in direction at 4.4 mV. In addition, the channels showed K + selectivity, in that the reversal potential shifted in a manner similar to that predicted by the Nernst potential for K + . Barium (1 mM) applied to the intracellular face of the channel produced a voltage-dependent block and external tetraethylammonium (TEA; at 1 mM) caused a large reduction in the unitary current amplitude. Taken together, these observations indicate that the channel most closely resembled BK Ca . 3 In ®ve out of six inside-out patches, NO (45 or 67 mM) produced an increase in BK Ca activity. In inside-out patches, BK Ca activity was also enhanced in some patches with 100 or 200 mM 3-morpholinosydnonimine (SIN-1) (4/11) and 100 mM sodium nitroprusside (SNP) (3/8). The variability in channel opening with the NO donors may re¯ect variability in the release of NO from these compounds. 4 In inside-out patches, 100 mM SIN-1 failed to increase BK Ca activity (in all 4 patches tested), while at a higher (500 mM) concentration SIN-1 had a direct blocking e ect on the channels (n=3). NO applied directly to inside-out patches increased (P50.05) BK Ca activity in two patches. 5 In the majority of cells (6 out of 7), application of NO (45 or 67 mM) evoked an increase in the amplitude of whole-cell currents in perforated patches. This action was not a ected by the soluble guanylyl cyclase inhibitor, 1H-[1,2,4] oxadiazolo [4,3-a]quinoxalin-1-one (ODQ). An increase in wholecell current was also evoked with either of the NO donors, SIN-1 or SNP (each at 100 mM). With SIN-1, the increase in current was blocked with the BK Ca channel blocker, iberiotoxin (50 nM). 6 With conventional whole-cell voltage clamp, the increase in the outward K + current evoked with SIN-1 (50 ± 300 mM) showed considerable variability. Either no e ect was obtained (11 out of 18 cells), or in the remaining cells, an average increase in current amplitude of 38.7+10.2% was recorded at 40 mV. 7 In cell-attached patches, large conductance voltage-dependent K + channels were stimulated by SIN-1 (100 mM) applied to the cell (n=5 patches). 8 These data indicate that NO and its donors can directly stimulate BK Ca activity in cells isolated from the rat mesenteric artery. The ability of NO directly to open BK Ca channels could play an important functional role in NO-induced relaxation of the vascular smooth muscle cells in this small resistance artery.

A Catalytically Inactive Mutant of Type I cGMP-dependent Protein Kinase Prevents Enhancement of Large Conductance, Calcium-sensitive K+ Channels by Sodium Nitroprusside and cGMP

“…These results are further consistent with the observed phenotype of cGKI-deficient knockout mice, which display impaired endothelium and NO-dependent relaxation of smooth muscle, resulting in vascular and intestinal dysfunction (45,47). The question of whether NO and NO donors may also be able to directly activate BK Ca channels is not supported by our data and remains controversial (55)(56)(57)(58); it is possible that such a phenomenon may depend upon the specific preparation in use, along with the types and concentrations of agents under study.…”

Vasorelaxation Induced by a New Naphthoquinone-Oxime is Mediated by NO-sGC-cGMP Pathway

“…In addition, the mechanisms underlying the effects of exogenous nitrovasodilators are predominantly mediated by cyclic guanosine monophosphate (cGMP), as a result of the activation of soluble guanylyl cyclase [17,18]. Cyclic GMP may cause vasodilation by the stimulation of cyclic nucleotide-gated channels [19]. Therefore, we suggest that the decrease in blood pressure elicited by Oxime S1 under our experimental conditions could be due to NO release in vascular smooth muscle cells.…”

Nitric Oxide–Dependent Feedback Loop Regulates Transient Receptor Potential Vanilloid 4 (TRPV4) Channel Cooperativity and Endothelial Function in Small Pulmonary Arteries

“…NO can alter the activity of several ion channels by S ‐nitrosylation or activation of guanylyl cyclase‐protein kinase G (GC‐PKG) signaling 13, 14, 15, 16, 17. In cultured cells, S ‐nitrosylation of TRPV4 channels increased the channel function,18 and activation of GC‐PKG signaling reduced the channel activity 19.…”