Characterization of an apamin‐sensitive small‐conductance Ca²⁺‐activated K⁺ channel in porcine coronary artery endothelium: relevance to EDHF

Abstract

1 The apamin-sensitive small-conductance Ca 2+ -activated K + channel (SK Ca ) was characterized in porcine coronary arteries. 2 In intact arteries, 100 nM substance P and 600 mM 1-ethyl-2-benzimidazolinone (1-EBIO) produced endothelial cell hyperpolarizations (27.8+0.8 mV and 24.1+1.0 mV, respectively). Charybdotoxin (100 nM) abolished the 1-EBIO response but substance P continued to induce a hyperpolarization (25.8+0.3 mV).3 In freshly-isolated endothelial cells, outside-out patch recordings revealed a unitary K + conductance of 6.8+0.04 pS. The open-probability was increased by Ca 2+ and reduced by apamin (100 nM). Substance P activated an outward current under whole-cell perforated-patch conditions and a component of this current (38%) was inhibited by apamin. A second conductance of 2.7+0.03 pS inhibited by d-tubocurarine was observed infrequently. 4 Messenger RNA encoding the SK2 and SK3, but not the SK1, subunits of SK Ca was detected by RT ± PCR in samples of endothelium. Western blotting indicated that SK3 protein was abundant in samples of endothelium compared to whole arteries. SK2 protein was present in whole artery nuclear fractions. 5 Immuno¯uorescent labelling con®rmed that SK3 was highly expressed at the plasmalemma of endothelial cells and was not expressed in smooth muscle. SK2 was restricted to the peri-nuclear regions of both endothelial and smooth muscle cells. 6 In conclusion, the porcine coronary artery endothelium expresses an apamin-sensitive SK Ca containing the SK3 subunit. These channels are likely to confer all or part of the apamin-sensitive component of the endothelium-derived hyperpolarizing factor (EDHF) response.

Reduced expression of SK3 and IK1 channel proteins in the cavernous tissue of diabetic rats

“…Expression of IK1, SK2 and SK3 mRNA can be detected by RT-PCR. The SK3 protein is abundant in porcine coronary endothelial cells, and immunofluorescent labelling confirms that IK1 and SK3 are expressed at the plasmalemma of porcine coronary endothelial cells [21]. In addition, it is well documented that in a number of cell types such as lymphocytes [22] and fibroblasts [23,24], IK1 expression is highly variable during the different phases of cell proliferation.…”

Mineralocorticoid receptor is involved in rat and human ocular chorioretinopathy

“…For example, the calcium-activated K channel KCa2.3 has previously been implicated in vasodilation (14,15). Since aldosterone/MR activation is known to modulate ion channel expression in other tissues (16)(17)(18), we reasoned that KCa2.3 might be involved in aldosterone/MR-induced choroidal vasodilation.…”

Thromboxane receptor stimulation associated with loss of SKCa activity and reduced EDHF responses in the rat isolated mesenteric artery

“…Riluzole is an opener of SK Ca channels, although it has other effects, such as inhibition of Na þ channels and twin-pore domain K channels (Taylor & Meldrum, 1995;Song et al, 1997;Duprat et al, 2000). The SK Ca channels are restricted to the endothelium, as they are in other arteries (Marchenko & Sage, 1996;Edwards et al, 1998;Mistry & Garland, 1998a, b;Burnham et al, 2002;Eichler et al, 2003).…”