Evidence for voltage-sensitive, calcium-conducting channels in airway epithelial cells

In airways epithelial cultures, mechanical stimulation induces intracellular Ca2+ concentration ([Ca2+]i) changes by causing Ca2+ entry and intracellular Ca2+ release. Mechanically induced Ca2+ fluxes across the plasma membrane are blocked by Ni2+ (Boitano, S., M. J. Sanderson, and E. R. Dirksen. J. Cell. Sci. 107: 3037-3044, 1994). In this report we use fluorescence imaging microscopy with fura 2 and intracellular recording of the transmembrane potential to further characterize Ca2+ flux in the plasma membrane of these cells. Mechanically induced Ca2+ influx is blocked by nifedipine. Addition of the dihydropyridine agonist BAY K8644 (2 microM) leads to a delayed increase of [Ca2+]i that is dependent on extracellular Ca2+. Switching to high extracellular K+ concentration ([K+]o) causes depolarization of the plasma membrane and a transient increase in [Ca2+]i. The number of cells that respond to high [K+]o is significantly decreased by Ni2+ (1 mM) or nifedipine (10 microM). Mechanical stimulation causes a rapid depolarization of the stimulated cell that can be suppressed by the K+ ionophore valinomycin. Valinomycin treatment also blocks mechanically induced Ca2+ dux. These results suggest that voltage-sensitive Ca(2+)-conducting channels exist in airway epithelial cells, and these channels contribute to the [Ca2+]i changes observed after mechanical stimulation or depolarization of the plasma membrane.