Use of intermediate/small conductance calcium-activated potassium-channel activator for endothelial protection

Objectives: Endothelial dysfunction occurs in hypoxia-related states such as ischemic heart disease or heart surgery. Intermediate-and small-conductance calcium-activated potassium channels (IKCa and SKCa) are closely related to endothelium-dependent hyperpolarizing factor-mediated endothelial function. However, the status of these K-Ca under hypoxia is unknown. We investigated whether endothelial dysfunction under hypoxic state is related to the alterations of IKCa and SKCa and whether use of IKCa/SKCa activator may protect endothelium from hypoxia-reoxygenation injury. Methods: Isometric tension measurement, patch-clamp technique, intracellular membrane potential recording, and molecular methods were used to study porcine coronary arteries and endothelial cells. Results: Hypoxia-reoxygenation (60-30 minutes) decreased endothelium-dependent hyperpolarizing factor-mediated relaxation at normothermia in Krebs solution (43.3% +/- 6.3% vs 82.3% +/- 2.9%) and in St Thomas' Hospital cardioplegic solution (28.9% +/- 1.8% vs 78.1% +/- 3.0%) (P < .001) as well as at hypothermia in St Thomas' Hospital solution (43.1% +/- 2.6%, P < .001). Hypoxia-reoxygenation markedly reduced endothelial IKCa (2.8 +/- 0.6 vs 6.9 +/- 0.6 pA/pF) and SKCa currents (1.5 +/- 0.3 vs 4.3 +/- 0.4 pA/pF) (P < .05) and down-regulated endothelial IKCa expression. IKCa/SKCa activator 1-ethyl-2-benzimidazolinone enhanced K+ current in endothelial cells that was blunted by hypoxia. Further, 1-ethyl-2-benzimidazolinone restored (P < .001) endothelium-dependent hyperpolarizing factor-mediated relaxation with hyperpolarization recovered from 6.0 +/- 0.3 to 7.8 +/- 0.4 mV (P < .05). Conclusions: In porcine coronary arteries, hypoxia markedly reduced endothelial K+ currents related to IKCa and SKCa with downregulation of protein expression and endothelium-derived hyperpolarizing factor function. IKCa/SKCa activator may preserve endothelium-dependent hyperpolarizing factor-mediated relaxation with enhancement of K+ current in endothelial cells and cellular membrane potential hyperpolarization in smooth muscle cells and may become a new strategy to protect coronary endothelium in cardiac surgery or transplantation. (J Thorac Cardiovasc Surg 2011;141:501-10)