CYTOSOLIC CA2-CYCLASE RESPONSES IA PHENOTYPICALLY DISTINCT PULMONARY ENDOTHELIAL-CELLS( AND ADENYLYL)

Pulmonary microvascular endothelium forms a tighter barrier than does pulmonary artery endothelium; the mechanism of this important phenotyp ic difference is uncertain. We examined two regulators of endothelial permeability, cytosolic Ca2+ concentration ([Ca2+](i)) and adenosine 3 ',5'-cyclic monophosphate (cAMP), in microvascular (PMVEC) and pulmona ry conduit artery (PAEC) endothelium. Both resting and stimulated [Ca2 +](i) were lower in PMVEC compared with PAEC (resting [Ca2+](i), 94 +/ - 7 vs. 123 +/- 8 nM; ATP-stimulated peak, 1.04 +/- 0.14 vs. 1.98 +/- 0.13 mu M). Sustained Ca2+ transients in response to either ATP or tha psigargin were reduced in PMVEC compared with PAEC (ATP, 199 +/- 22 vs . 411 +/- 43 nM; thapsigargin, 195 +/- 13 vs. 527 +/- 65 nM), suggesti ng reduced Ca2+ influx in PMVEC. Reduced Ca2+ in flux in PMVEC was con firmed by Mn2+ quenching and patch-clamp experiments. mRNA for Ca2+-in hibitable and protein kinase C-stimulated adenylyl cyclases was detect ed in both cell types. Whereas ATP caused a [Ca2+](i)-mediated decreas e in cAMP in PAEC, ATP caused a protein kinase C-mediated increase in cAMP in PMVEC. We conclude that PMVEC express a unique phenotype that favors enhanced barrier function through attenuated Ca2+ influx and pr eservation of cAMP content.