Studies on Ion Channels of Coronary Endothelium with Clinical Implications

Ca2+-activated potassium channels (KCa) and canonical transient receptor potential (TRPC) channels are essential to endothelial function. In ischemic heart disease, or in cardiac surgery, coronary endothelium is subjected to ischemia-reperfusion (I-R) / hypoxia-reoxygenation (H-R) injury. Hyperkalemic cardioplegic or organ preservation solutions used in cardiac surgery including heart transplantation also impair endothelial function. The present study was designed to mainly investigate whether endothelial dysfunction occurring in H-R or in hyperkalemic exposure is attributable to alterations of intermediate- and small-conductance KCa (IKCa and SKCa) channels, or TRPC channels, in particular, the TRPC3 channel.;Whole-cell membrane currents of IKCa, SKCa, or TRPC3 were recorded by patch-clamp in primary cultured porcine coronary endothelial cells (PCECs). TRPC3 current was also studied in human embryonic kidney cells (HEK293 cells) transiently overexpressed with TRPC3 gene. Protein or mRNA expression of these channels was detected by Western blot or RT-PCR. Intracellular Ca2+ concentration was measured by Ca2+ imaging technique. Isometric force study was performed in a wire myograph and endothelial nitric oxide (NO) release was measured electrochemically by using a NO-specific microsensor in porcine coronary small arteries.;Exposure to 60-min hypoxia followed by reoxygenation inhibited the vasorelaxant response of coronary arteries to IKCa / SKCa activator 1-EBIO. H-R reduced endothelial IKCa and SKCa currents and downregulated IKCa expression in PCECs. 1-EBIO enhanced endothelial K+ current that was blunted by H-R.;In TRPC3-overexpressing HEK293 cells, followed by reoxygenation, short-time hypoxia (10-min) enhanced, whereas prolonged hypoxia (60-min) reduced the current induced by TRPC3/6/7 activator OAG.;In PCECs, hypoxia for 60-min with reoxygenation reduced TRPC3 current and Ca2+ influx via TRPC3, which was accompanied by decreased NO release and endothelium-dependent vasorelaxation of porcine coronary arteries. The compromised endothelial function was restored by OAG. The translocation of TRPC3 to endothelial membrane was inhibited by H-R.;Exposure to hyperkalemic solutions decreased Ca2+ influx via TRPC3 in PCECs. The reduced Ca2+ influx in PCECs and the attenuated EDHF-mediated vasorelaxation in porcine coronary arteries, which were caused by hyperkalemic or cardioplegic / organ preservation solutions, were restored by OAG.;Our results indicate that: (1) Endothelial IKCa, SKCa and TRPC3 play an important role in regulating vascular tone; TRPC3 contributes to NO release from endothelial cells and is also involved in the function of EDHF. (2) H-R (60-30 min) reduces endothelial IKCa and SKCa currents with downregulation ofthe protein expression of IKCa. (3) H-R has dual effect on TRPC3 with short-time hypoxia (lO-min) enhancing whereas prolonged hypoxia (60-min) decreasing the electrophysiological activity of this channel. H-R (60-30 min) inhibits the translocation of TRPC3 to endothelial membrane. Furthermore, H-R inhibits Ca2+ influx via TRPC3 and such inhibition is associated with a decrease of NO production. (4) The activator of IKCa / SKCa or TRPC protects coronary endothelium against H-R injury. In coronary endothelium exposed to hyperkalemic or cardioplegic / organ preservation solutions, TRPC activator also exhibits protective effect.;The above findings are likely to have significant implications in ischemic heart disease and in modern cardiopulmonary surgery.