Impaired hyperpolarization in regenerated endothelium after balloon catheter injury

Ca2+-activated K+ (K-Ca) channels control endothelial Ca2+ homeostasis and the formation of vasodilators. After angioplasty, dysfunction of the regenerated endothelium, leads to abnormal vasoregulation. In this study, we tested the expression and function of K-Ca channels in regenerated endothelium at 6 weeks after balloon catheter injury of rat carotid arteries (CAs) by using single-cell reverse transcription-polymerase chain reaction, patch-clamp techniques, and analysis of vasoreactivity. In single regenerated endothelial cells (ECs), the percentage of ECs expressing the K-Ca genes, rSK3 (12 +/-8%) and rIK1 (22 +/-9%), was significantly lower compared with the percentage of native ECs expressing these genes (rSK3 58 +/-8%, rIK1 64 +/- 10%). In patch-clamp experiments, K-Ca currents and acetylcholine-induced hyperpolarization were markedly reduced in regenerated ECs (shift of membrane potential -6 +/-3 mV) compared with those in native ECs (shift of membrane potential -21 +/-5 mV). In pressure myograph experiments, acetylcholine-induced dilation was impaired in reendothelialized CAs compared with normal CAs. Intraluminal application of the K-Ca blocker apamin and charybdotoxin inhibited dilation by 30% in normal CAs but was without effect in reendothelialized CAs. Intraluminal application of 1-ethyl-2-benzimidazolinone (100 mu mol/L), an opener of K-Ca channels, evoked dilation by 29% in normal CAs but had no effect in reendothelialized CAs. In conclusion, the impaired expression of K-Ca channels in regenerated endothelium results in defective hyperpolarization and impaired dilation. Thus, the impaired K-Ca channel function contributes to functional alterations of regenerated endothelium after angioplasty.