Sulfonylurea Receptor-Dependent and -Independent Pathways Mediate Vasodilation Induced by ATP-Sensitive K⁺ Channel Openers

Abstract

ATP-sensitive K ϩ (K ATP ) channel openers are vasodilators that activate both plasma membrane and mitochondrial K ATP channels. Here, we investigated the molecular mechanisms by which diazoxide and pinacidil induce vasodilation by studying diameter regulation of wild-type [SUR2(ϩ/ϩ)] and sulfonylurea receptor (SUR) 2-deficient [SUR2(Ϫ/Ϫ)] mouse myogenic mesenteric arteries. Ryanodine (10 M), a ryanodine-sensitive Ca 2ϩ release (RyR) channel blocker; iberiotoxin (100 nM), a large-conductance Ca 2ϩ -activated K ϩ (K Ca ) channel blocker; 4-aminopyridine (4-AP; 1 mM), a voltage-gated K ϩ (K V ) channel blocker; manganese(III) tetrakis(1-methyl-4-pyridyl)porphyrin (MnTMPyP; 100 M), an antioxidant; and a combination of ryanodine and 4-AP reduced diazoxide (100 M)-induced dilation in pressurized (60 mm Hg) SUR2(ϩ/ϩ) arteries by 45 to 77%. In contrast, these inhibitors did not alter pinacidil (5 M)-induced dilation in SUR2(ϩ/ϩ) arteries. Reverse transcription-polymerase chain reaction indicated that SUR2B was the only SUR isoform expressed in SUR2(ϩ/ϩ) mesenteric artery smooth muscle cells, whereas SURs were absent in SUR2(Ϫ/Ϫ) cells. In SUR2(Ϫ/Ϫ) arteries, pinacidil-induced vasodilation was ϳ10% of that in SUR2(ϩ/ϩ) arteries, whereas diazoxide-induced vasodilation was similar in SUR2(ϩ/ϩ) and SUR2(Ϫ/Ϫ) arteries. Atpenin (1 M), a selective electron transport chain (ETC) complex II inhibitor, dilated arteries similarly to diazoxide, and this effect was attenuated by MnTMPyP and ryanodine ϩ 4-AP. Atpenin also attenuated diazoxide-, but not pinacidil-induced vasodilation. In summary, data indicate that pinacidil-induced vasodilation requires SUR2B, whereas diazoxide-induced vasodilation does not require SURs. Rather, diazoxide-induced vasodilation involves ETC II inhibition; a smooth muscle cell-reactive oxygen species elevation; and RyR, K Ca , and K V channel activation. These data indicate that K ATP channel openers regulate arterial diameter via SUR-dependent and -independent pathways.Plasma membrane ATP-sensitive K ϩ (pmK ATP ) channels couple changes in cellular metabolic activity to membrane electrical excitability (Ashcroft and Ashcroft, 1990). K ATP channels are composed of pore-forming K ir 6.x and regulatory sulfonylurea receptor (SUR) subunits . The assembly of four K ir 6.x and four SUR subunits results in tissue-specific K ATP channel complexes with different functional, electrophysiological, and pharmacological properties .SURs are members of the ATP-binding cassette transporter protein superfamily that are predicted to form 17 transmembrane-spanning helices and two intracellular nucleotide binding domains (Tusná dy et al., 1997). Two distinct SUR isoforms (SUR1 and SUR2) have been identified that are ϳ70% identical . Alternative splicing of the SUR2 gene at the 3Ј end results in two additional isoforms, SUR2A and SUR2B, that have different pharmacological profiles (Isomoto et al., 1996). SURs are the molecular target of pharmacologically diverse and clinically important agonists and antagonists. ...

Vasodilation induced by oxygen/glucose deprivation is attenuated in cerebral arteries of SUR2 null mice

“…Spindle-shaped arterial smooth muscle cells were manually collected under an inverted Nikon TS 100 microscope by aspirating them into a borosilicate glass micropipette, yielding pure cell preparations as we have done previously (1). Approximately 100 cells were used for each RT-PCR experiment.…”

“…cDNA was synthesized from RNA samples using iScript cDNA Synthesis kit (Bio-Rad; Hercules, CA). cDNA products were amplified by nested PCR using our previously designed gene-specific oligonucleotide primer pairs (1). Specific primers for first-round and nested-PCR amplification of SUR1 were designed to generate cDNA fragments of 413 and 169 bp, respectively (1).…”

“…Vascular myocyte plasma membrane K ATP channels are comprised of inwardly rectifying K ϩ channel 6.1 (Kir6.1) and sulfonylurea receptor (SUR)-2B subunits (1,27). Mitochondrial K ATP (mitoK ATP ) channels have also been described, but their molecular composition and physiological functions in vascular myocytes are unclear (29).…”

“…Furthermore, the effects of K ATP channel blockers may be modified by endogenous regulators of signal transduction, including cellular metabolism (40). To investigate the physiological functions of K ATP channels in mediating hypoxia-and OGD-induced vasodilation, we studied cerebral arteries of both SUR2 nl mice, in which myocyte SUR2-containing K ATP channels are abolished, and humans (1,4,16,37).…”

Alternative splicing of Cav1.2 channel exons in smooth muscle cells of resistance-size arteries generates currents with unique electrophysiological properties

“…Cardiac myocytes were kindly provided by Dr. P. A. Hofmann in the Department of Physiology at UTHSC. Arterial or cardiac myocytes were manually collected under an inverted microscope, yielding pure cell preparations (2,7,16).…”