Maxi-K+ channel beta1 expression in sleep apnea patients and its modulation by CPAP treatment.

BACKGROUND: Maxi-K(+) channels play a major vasodilator role in the regulation of arterial tone. Hypoxia downregulates the expression of the maxi-K(+) channel beta1-subunit in rat and human arterial myocytes, thus facilitating vasoconstriction. We have investigated the relationships among hypoxemia, arterial pressure, and the expression of the beta1-subunit in patients with severe obstructive sleep apnea-hypopnea syndrome (SAHS), a highly prevalent condition that predisposes to hypertension. METHODS: We studied 20 male patients with strong clinical suspicion of SAHS. Overnight polysomnography and 24-h ambulatory blood pressure monitoring were performed in each patient. Evaluation of beta1-subunit mRNA expression was made by a simple blood test using peripheral blood leukocytes (PBLs). The last two determinations were repeated 3 months after initiation of continuous positive airway pressure (CPAP) treatment. RESULTS: In untreated obstructive SAHS patients, beta1-subunit mRNA levels were correlated with the minimum level of overnight blood O(2) saturation (r(2) = 0.56, P < 0.05) and systolic arterial pressure (r(2) = 0.64, P < 0.01). Notably, the correction of nocturnal hypoxemia with CPAP resulted in upregulation of beta1-subunit mRNA and to a parallel significant decrease of systolic and diastolic arterial pressures of 6.5 and 5.3 mm Hg, respectively. CONCLUSIONS: These observations, although preliminary, suggest that the maxi-K(+) beta1-subunit could contribute to vascular dysregulation in SAHS patients. Leukocyte beta1 expression may be an independent readout of hypoxemia that could be useful as molecular marker for impending hypertension.

Role of peroxynitrite in endothelial damage mediated by Cyclosporine A.

Although Cyclosporine A (CsA) is an effective therapy for immunosuppression, its use encompasses serious side effects that have been associated with oxidative stress. We previously reported the intracellular formation of both peroxynitrite and 3-nitrotyrosine in cultured bovine aortic endothelial cells (BAEC) when exposed to CsA. Here we show that re-addition of CsA to BAEC increases peroxynitrite formation in a concentration-dependent manner. This effect is inhibited by the glutathione donor and antioxidant, N-acetylcysteine (NAC). BAEC exposed to CsA showed impaired integrity of plasma membranes and increased cytolysis, a phenomenon prevented by NAC. When CsA was administered to mice, the increased presence of 3-nitrotyrosine was detected in the aortic endothelium, an effect also abrogated by the concomitant administration of NAC. An increase in nitrated MnSOD was detected in BAEC treated with CsA and the peroxynitrite donor SIN-1 and recapitulated in recombinant MnSOD, exposed to the conditioned media from BAEC. We propose that CsA promotes nitration of specific molecular targets, such as MnSOD, within vascular endothelial cells. This may represent a pathogenetic mechanism of vascular injury. Inhibition of this process by clinically applicable antioxidants, such as NAC, lends a basis for the exploration of therapeutic alternatives in patients treated with CsA.

Decreased expression of maxi-K+ channel beta1-subunit and altered vasoregulation in hypoxia.

BACKGROUND: Hypertension, a major cause of cardiovascular morbidity and mortality, can result from chronic hypoxia; however, the pathogenesis of this disorder is unknown. We hypothesized that downregulation of the maxi-K+ channel beta1-subunit by hypoxia decreases the ability of these channels to hyperpolarize arterial smooth muscle cells, thus favoring vasoconstriction and hypertension. METHODS AND RESULTS: Lowering O2 tension produced a decrease of maxi-K+ beta1-subunit mRNA levels in rat (aortic and basilar) and human (mammary) arterial myocytes. This was paralleled by a reduction of the beta1-subunit protein level as determined by immunocytochemistry and flow cytometry. Exposure to hypoxia also produced a decrease of open probability, mean open time, and sensitivity to the xenoestrogen tamoxifen of single maxi-K+ channels recorded from patch-clamped dispersed myocytes. The number of channels per patch and the single-channel conductance were not altered. The vasorelaxing force of maxi-K+ channels was diminished in rat and human arterial rings exposed to low oxygen tension. CONCLUSIONS: These results indicate that a decrease of the maxi-K+ channel beta1-subunit expression in arterial myocytes is a key factor in the vasomotor alterations induced by hypoxia.

Superoxide limits cyclosporine-A-induced formation of peroxynitrite in endothelial cells(2).

Peroxynitrite (ONOO(-)) is a potent oxidant formed by the nonenzymatic reaction between superoxide anion (O(2)(*-)) and nitric oxide (NO*) in a one-to-one stoichiometry. Accumulated evidence suggests that endothelial dysfunction coincides with an enhanced NO* synthase expression and O(2)(*-) production, facilitating ONOO(-) formation. In vivo, formation of ONOO(-) has been associated with atherosclerosis and vascular aging. The immunosuppressor Cyclosporine A (CsA) has been associated to human endothelial dysfunction and accelerated atherosclerosis. We have previously shown that CsA induced a transcriptionally mediated increase of the eNOS gene expression and that CsA induced the formation of nitric oxide, O(2)(*-), and ONOO(-) in vascular endothelial cells. In this work, we evaluate the CsA-induced relative amounts of formation of O(2)(*-) and NO*, providing data consistent with a role of O(2)(*-), and not NO*, as the limiting factor in the CsA-dependent intracellular formation of ONOO(-) in vascular endothelial cells. Furthermore, when endothelial cells were treated with CsA in a situation of increased generation of superoxide such as that provided by high glucose levels, a further increase in the formation of peroxynitrite was detected. The temporal availability of O(2)(*-) for peroxynitrite formation may thus become critical in the pathophysiological scenarios where reactive nitrogen intermediates are operative.