Functional effects of expression of hslo Ca 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 (BK_Ca) in an endothelial cell type normally lacking this channel. The human homologue hslo of BK_Ca was expressed in cultured bovine pulmonary artery endothelial (CPAE) cells, which have no endogenous BK_Ca. 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 CI⁻ current (I_cl,ca). The most prominent current component during ATP stimulation in hslo expressing cells was conducted 13K Ca which resulted in a pronounced transient hyperpolarization. This hyperpolarization, which was absent in non-transfected cells, was enhanced if I_Cl,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 BK_Ca exerts a positive feedback on Ca²⁺ signals in endothelial cells by counteracting the negative (depolarizing)effect of stimulation of Ca²⁺-activated CI⁻ channels.