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 regene rated endothelium, leads to abnormal vasoregulation. In this study, we test ed the expression and function of K-Ca channels in regenerated endothelium at 6 weeks after balloon catheter injury of rat carotid arteries (CAs) by u sing single-cell reverse transcription-polymerase chain reaction, patch-cla mp techniques, and analysis of vasoreactivity. In single regenerated endoth elial cells (ECs), the percentage of ECs expressing the K-Ca genes, rSK3 (1 2 +/-8%) and rIK1 (22 +/-9%), was significantly lower compared with the per centage of native ECs expressing these genes (rSK3 58 +/-8%, rIK1 64 +/- 10 %). In patch-clamp experiments, K-Ca currents and acetylcholine-induced hyp erpolarization 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-ind uced dilation was impaired in reendothelialized CAs compared with normal CA s. Intraluminal application of the K-Ca blocker apamin and charybdotoxin in hibited dilation by 30% in normal CAs but was without effect in reendotheli alized 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 b ut had no effect in reendothelialized CAs. In conclusion, the impaired expr ession of K-Ca channels in regenerated endothelium results in defective hyp erpolarization and impaired dilation. Thus, the impaired K-Ca channel funct ion contributes to functional alterations of regenerated endothelium after angioplasty.