Ion transport by canine tracheal mucosa: effect of elevation of cellular calcium

Calcium is considered to be modulator of paracellular shunt pathway as well as several cell functions such as ion transport. We used calcium ionophore A23187 to study effect of mobilization of calcium on chloride and sodium transport in canine tracheal epithelium. This epithelium secretes Cl and absorbs Na under short-circuit conditions. Sheets of canine tracheal mucosa were mounted in chambers, perfused with Krebs-Henseleit solution at 37 degrees C and oxygenated. Unidirectional fluxes of 22Na and 36Cl were measured in matched paired mucosae under short-circuit conditions. Net flux of each ion was calculated from these unidirectional fluxes, before and after addition of A23187 (10(-6) M) to submucosal bath. Short-circuit current and potential difference were measured. From these values conductance was calculated. Initially, short-circuit current, potential difference, and conductance were 31 +/- 8 microA/cm(2), 26 +/- 4 mV, and 1.2 +/- 0.2 mS/cm(2), respectively, and increased significantly after A23187 to 76 +/- 20 microA/cm(2), 41 +/- 5 mV, and 1.8 +/- 0.4 mS/cm(2), respectively (mean +/- SE for 10 tissues). Net Cl secretion increased from 0.83 +/- 0.23 muEq/cm(2) hr to 2.84 +/- 0.38 muEq/cm(2) hr (P less than .002) and net Na absorption of 0.50 +/- 0.14 muEq/cm(2) hr was abolished (P less than .02). These data show that increase in cellular levels of calcium increases chloride secretion and abolishes sodium transport. Intracellular calcium appears to regulate cell membrane permeability to chloride and sodium.U