Functional effects of expression of hslo Ca2+ activated K+ channels in cultured macrovascular endothelial cells

The aim of the present study is to elucidate the effects of the expression of large conductance Ca2+ activated K+ channels (BKca) in an endothelial cell type normally lacking this channel. The human homologue hslo of BKCa was expressed in cultured bovine pulmonary artery endothelial (CPAE) cells, which have no endogenous BKCa Membrane potential, ionic currents and Ca2+ signals were investigated in non-transfected and transfected cells using a combined patch clamp and Fura-2 fluorescence technique. In non-transfected control CPAE cells, ATP evoked a Ca2+ activated Cl(-)current (I-Cl,I-Ca). The most prominent current component during ATP stimulation in hslo expressing cells was conducted BKCa which resulted in a pronounced transient hyperpolarization. This hyperpolarization, which was absent in non-transfected cells, was enhanced if I-Cl,I-Ca was blocked with niflumic acid, The sustained component of the Ca2+ response during ATP stimulation was significantly larger in hslo transfected cells than in non-transfected cells. This plateau level correlated well with the corresponding effects of ATP on the membrane potential, indicating that the expression of cloned BKCa exerts a positive feedback on Ca2+ signals in endothelial cells by counteracting the negative (depolarizing)effect of stimulation of Ca2+-activated Cl(-)channels.