Impaired Function and Expression of Endothelial Small Ca2+-Activated K Channels (SK3) in Reendothelialized Carotid Arteries After Balloon Catheter Injury (BCI)
Ca2+-activated K channels (KCa) play an important role in endothelial function by controlling the electrochemical driving force for Ca2+influx and subsequent formation of vasoactive factors like NO and EDHF. An altered endothelial function have been suggested to be present in reendothelialized arteries after balloon catheter injury (BCI). We compared expression and function of endothelial rSK3 in reendothelialized carotid artery (CA) after BCI and not injured contralateral CA (CON) by using single-cell RT-PCR and patch-clamp (PC) techniques. Male Sprague-Dawley rats underwent BCI of the right CA. After 6 weeks, neointima formation and reendothelialization were confirmed by morphological analysis. Single endothelial cells (EC) were directly harvested from the luminal wall with the patch pipette. cDNA of rSK3 was amplified along with cDNA of endothelial nitric oxide synthase (rNOSIII), an EC marker. The percentage of rNOSIII+-samples was not different between CON (84% ± 10) and injured CA (84% ± 6). Expression of rSK3 was detected in 50% ± 10 of rNOSIII+-EC from CON. From injured CA, expression of rSK3 was detected in only 3% ± 3 of NOSIII+-EC (P<0.05). In whole-cell PC experiments in EC from CON, cell dialysis with Ca2+induced K currents, which were sensitive to apamin, a blocker of SK3. In contrast, in EC from injured CA, cell dialysis with Ca2+did not activate K currents. In current-clamp PC measurements of EC membrane potential (Vm) of CON, acetylcholine (ACh) induced a sustained and apamin-sensitive hyperpolarization from a resting Vm of -19 ± 5 mV to 40 ± 13 mV (ΔVm -19 ± 7 mV). In injured CA, an ACh-induced hyperpolarization was not observed (-22 ± 7 mV, ΔVm 0 ± 1 mV). Resting Vm (22 ± 6 mV) was not different. In conclusion, the deficient expression of KCain reendothelialized injured CA abolishes endothelial hyperpolarization in response to humoral stimulation. The defective hyperpolarization presumably leads to a decreased Ca2+influx and subsequent synthesis of vasoactive factors. This might indicate a diminished function of the newly formed endothelium in CA after BCI.