Altered potassium ATP channel signaling in mesenteric arteries of old high salt-fed rats

Potassium channels in vascular smooth muscle: a pathophysiological and pharmacological perspective

Potassium (K⁺ ) ion channel activity is an important determinant of vascular tone by regulating cell membrane potential (MP). Activation of K⁺ channels leads to membrane hyperpolarization and subsequently vasodilatation, while inhibition of the channels causes membrane depolarization and then vasoconstriction. So far five distinct types of K⁺ channels have been identified in vascular smooth muscle cells (VSMCs): Ca⁺² -activated K⁺ channels (BK_{C a} ), voltage-dependent K⁺ channels (K_V ), ATP-sensitive K⁺ channels (K_ATP ), inward rectifier K⁺ channels (K_ir ), and tandem two-pore K⁺ channels (K₂ P). The activity and expression of vascular K⁺ channels are changed during major vascular diseases such as hypertension, pulmonary hypertension, hypercholesterolemia, atherosclerosis, and diabetes mellitus. The defective function of K⁺ channels is commonly associated with impaired vascular responses and is likely to become as a result of changes in K⁺ channels during vascular diseases. Increased K⁺ channel function and expression may also help to compensate for increased abnormal vascular tone. There are many pharmacological and genotypic studies which were carried out on the subtypes of K⁺ channels expressed in variable amounts in different vascular beds. Modulation of K⁺ channel activity by molecular approaches and selective drug development may be a novel treatment modality for vascular dysfunction in the future. This review presents the basic properties, physiological functions, pathophysiological, and pharmacological roles of the five major classes of K⁺ channels that have been determined in VSMCs.

KMUP-1 protects against streptozotocin-induced mesenteric artery dysfunction via activation of ATP-sensitive potassium channels

BACKGROUND

Diabetes mellitus is a metabolic disorder characterized by chronic hyperglycemia accompanied by impaired vascular and endothelial function. Activation of ATP-sensitive potassium (K_ATP) channels can protect endothelial function against hypertension and hyperglycemia. KMUP-1, a xanthine derivative, has been demonstrated to modulate K⁺-channel activity in smooth muscles. This study investigated protective mechanisms of KMUP-1 in impaired mesenteric artery (MA) reactivity in streptozotocin (STZ)-induced diabetic rats.

METHODS

Rats were divided into three groups: control, STZ (65 mg/kg, ip) and STZ + KMUP-1 (5 or 10 mg/kg/day, ip). MA reactivity was measured by dual wire myograph. MA smooth muscle cells (MASMCs) were enzymatically dissociated and the K_ATP currents recorded by a whole-cell patch-clamp technique.

RESULTS

STZ decreased MA K_ATP currents in a time-course dependent manner and achieved steady inhibition at day 14. In the MASMCs of STZ-treated rats, KMUP-1 partially recovered the K_ATP currents, suggesting that vascular K_ATP channels were activated by KMUP-1. K⁺ (80 mM KCl)-induced MA contractions in STZ-treated rats were higher than those of control rats. KMUP-1 significantly attenuated STZ-stimulated MA contractions in response to high K⁺, suggesting that KMUP-1 may partly restore the vascular reactivity of MAs. In addition, STZ decreased the expression of endothelial nitric oxide synthase (eNOS) and this effect was reversed by KMUP-1, suggesting that KMUP-1 could improve STZ-induced vascular endothelial dysfunction.

CONCLUSION

KMUP-1 prevents STZ impairment of MA reactivity, eNOS levels and K_ATP channels, and accordingly protects against vascular dysfunction in diabetic rats.