[Ca2+]i changes in guinea pig tracheal smooth muscle cells in culture: effects of Na+ and ouabain

The objective of this work was to confirm that the contractile effects of ouabain and Na+-free solutions in guinea pig tracheal rings are associated with increments in the cytosolic free Ca2+ concentration ([Ca2+]i) in cultured tracheal smooth muscle (TSM) cells. Cultured cells were α-actin positive. Histamine (50 μM) and Na+-free solution elicited a transient increase in [Ca2+]i, while the responses to thapsigargin (1 μM) and ouabain (1 mM) were long lasting. However, carbachol (10, 200, and 500 mM) and high K+-solution produced no effect on [Ca2+]i, suggesting that cultured guinea pig TSM cells display a phenotype change but maintain some of the tracheal rings physiological properties. The transient rise in [Ca2+]i in response to the absence of extracellular Na+ and the effect of ouabain may indicate the participation of the Na+/Ca2+ exchanger (NCX) in the regulation of [Ca2+]i.