Gap junctional communication controls the overall endothelial calcium response to vasoactive agonists.

AIMS: A cytosolic calcium (Ca(2+)(i)) increase is an important activation signal for the endothelium. We investigated whether interendothelial spreading of the Ca(2+) signal via gap junctions (GJs) plays a role for the overall Ca(2+)(i) increase in response to vasoactive agonists. METHODS AND RESULTS: In human umbilical vein endothelial cells (HUVECs), a Ca(2+)(i) increase (Fura2) in response to histamine or ATP occurred initially only in about 30% of the cells (initially responding cells) reflecting the cell fraction expressing H(1) or purinergic receptors (FACS/immunohistochemistry). In the remaining adjacent cells, Ca(2+)(i) increases occurred only after a delay of up to 5 s. Blockade of GJ communication (meclofenamic acid and heptanol, or H(2)O(2); verified by dye injection) did not affect responses in the initially responding cells but abolished the delayed Ca(2+)(i) response of the remaining adjacent cells. The resulting reduction in the global endothelial Ca(2+)(i) response significantly reduced the nitric oxide synthesis (assessed as cGMP levels). Similar Ca(2+)(i) results were obtained in the endothelium of freshly isolated mouse (C57BL/6) aortas stimulated with ATP. The receptor-independent Ca(2+)(i) response to ionomycin occurred simultaneously in all cells, regardless of GJ inhibition. In separate experiments, inhibition of the IP(3) receptor (xestospongin-C; 40, µmol/L) but not of the ryanodine receptor (ryanodine, 250 µmol/L) reduced the spread of the Ca(2+)(i) signal into adjacent cells over longer distances. CONCLUSION: The global Ca(2+)(i) response of the endothelium to agonists is determined decisively by the functionality of GJs, thus establishing a new role for GJs in controlling endothelial activity and vasomotor function.

Early inflammatory response to asbestos exposure in rat and hamster lungs: role of inducible nitric oxide synthase.

Recent studies have suggested that inducible nitric oxide synthase (iNOS) plays a role in the development of asbestos-related pulmonary disorders. The pulmonary reactions of rats and hamsters upon exposure to asbestos fibers are well known to be disparate. In addition, in vitro experiments have indicated that mononuclear phagocytes from hamsters, in contrast to those from rats, lack the iNOS pathway. Therefore, the purpose of this study was to investigate whether rats and hamsters differ in lung iNOS expression in vivo upon exposure to asbestos fibers and whether differences in iNOS induction are associated with differences in the acute pulmonary inflammatory reaction. Body weight, alveolar-arterial oxygen difference, differential cell count in bronchoalveolar lavage fluid, total protein leakage, lung myeloperoxidase activity and lipidperoxidation, wet/dry ratio, iNOS mRNA and protein expression, and nitrotyrosine staining of lung tissue were determined 1 and 7 days after intratracheal instillation of asbestos fibers in CD rats and Syrian golden hamsters. Exposure of rats to asbestos fibers resulted in enhanced pulmonary iNOS expression and nitrotyrosine staining together with an acute inflammation that was characterized by an influx of neutrophils, enhanced myeloperoxidase activity and lipid peroxidation, damage of the alveolar-capillary membrane, edema formation, and impairment of gas exchange. In comparison, instillation of asbestos fibers in hamsters resulted in a significantly milder inflammatory reaction of the lung with no induction of iNOS in pulmonary cells. The data obtained provide important information to understand the underlying mechanisms of species differences in the pulmonary response upon exposure to asbestos fibers.