CA2-ACTIVATED CL- CURRENTS IN PULMONARY ARTERIAL MYOCYTES()

Currents from smooth muscle cells isolated from the pulmonary arterial tree of the rat were recorded under voltage clamp using the whole cel l configuration of the patch-clamp technique. Rapid increases in cytos olic free calcium evoked by flash photolysis of Nitr-5 activated a cur rent that, following ion substitution and pharmacological experiments, proved to be carried by Cl-. This current [I-Cl(Ca)] was evoked indep endently of photolytic by-products and, although smaller, was still ac tivated in the absence of pipette ATP. Experiments revealed that I-CI( Ca) was evoked in 80% of the cells isolated from the main pulmonary ar tery but only in 43% of the cells isolated from small vessels (200-400 mu m ID). Application of caffeine also resulted in activation of I-Cl (Ca), although the response current magnitude was larger in the main p ulmonary artery. Photolysis of Nitr-5 still activated I-Cl(Ca) in the presence of caffeine, suggesting that Ca2+ release is not a prerequisi te for activation of I-Cl(Ca). These results represent the first elect rophysiological recordings of Cl- currents from small pulmonary arteri al vessels and indicate that their Ca2+ regulation and/or distribution may be different throughout the pulmonary circulation.