FUNCTIONAL-EFFECTS OF EXPRESSION OF HSLO CA2-CELLS( ACTIVATED K+ CHANNELS IN CULTURED MACROVASCULAR ENDOTHELIAL)

The aim of the present study is to elucidate the effects of the expres sion of large conductance Ca2+ activated K+ channels (BKca) in an endo thelial cell type normally lacking this channel. The human homologue h slo of BKCa was expressed in cultured bovine pulmonary artery endothel ial (CPAE) cells, which have no endogenous BKCa Membrane potential, io nic currents and Ca2+ signals were investigated in non-transfected and transfected cells using a combined patch clamp and Fura-2 fluorescenc e technique. In non-transfected control CPAE cells, ATP evoked a Ca2activated Cl(-)current (I-Cl,I-Ca). The most prominent current compone nt during ATP stimulation in hslo expressing cells was conducted BKCa which resulted in a pronounced transient hyperpolarization. This hyper polarization, which was absent in non-transfected cells, was enhanced if I-Cl,I-Ca was blocked with niflumic acid, The sustained component o f the Ca2+ response during ATP stimulation was significantly larger in hslo transfected cells than in non-transfected cells. This plateau le vel correlated well with the corresponding effects of ATP on the membr ane potential, indicating that the expression of cloned BKCa exerts a positive feedback on Ca2+ signals in endothelial cells by counteractin g the negative (depolarizing)effect of stimulation of Ca2+-activated C l(-)channels.