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

In airway 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 K 8644 (2 mu M) 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 mu M). 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+ flux. These results suggest that voltage-sensitive Ca2+-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.