Altered ETB- but not ETA-receptor density and function in sheep airway smooth muscle cells in culture

The possibility that significant changes in endothelin (ET)A- and ETB-receptor density and function occur in airway smooth muscle cells (ASMCs) during cell growth and extended cell culture was investigated in sheep tracheal ASMCs. As in intact tracheal smooth muscle tissue from this species, early-passage sheep ASMCs contained a homogeneous population of ETA receptors. However, growth of ASMCs from seeding to postconfluence and repeated passage of ASMCs (6th to 14th passages) was associated with a substantial increase in ETB-receptor density, with no change in ETA-receptor density. ET-1-induced stimulation of ETB receptors increased the intracellular Ca2+ concentration in single ASMCs. Interestingly, a 2-day period of serum deprivation completely eliminated the increase in ETB-receptor density and the ETB receptor-mediated change in intracellular Ca2+ concentration. In summary, growth and repeated passage of sheep ASMCs were associated with a profound and selective increase in the density and function of the ETB receptor, a receptor subtype not present in early-passage ASMCs and not detected in intact sheep tracheal airway smooth muscle.