Nucleotide receptor-mediated decrease of tight-junctional permeability in cultured human cervical epithelium

Extracellular ATP changes the transepithelial electrical conductance (G(T)) across cultures of human cervical cells acutely, in a biphasic manner that is characterized by a rapid increase (phase I) followed by a sustained decrease in GT (phase II). We tested the hypothesis that the phase II response is mediated by decreases in the permeability of tight junctions. We studied the effect of ATP on the relative mobilities of Cl- vs. Na+ (u(Cl)/u(Na)) as calculated from changes in the dilution potential (V-dil). V-dil was induced by lowering NaCl from 130 to 10 mM in either the luminal or subluminal solutions bathing filters containing cells. u(Cl)/u(Na) was 1.27 across cervical cultures and 1.34 across blank filters, compared with a level of 1.52 in free solution. Increases in G(T) induced by transepithelial hydrostatic or hypertonic gradients (which increase permeability of lateral intercellular space) had no effect on u(Cl)/u(Na) Increases in G(T) induced by lowering extracellular Ca2+ to <0.1 mM increased u(Cl)/u(Na) to levels obtained in blank filters, indicating abrogation of tight-junctional resistance. Phase I response and ionomycin (which produces a sustained phase I-like increase in G(T)) had no effect on u(Cl)/u(Na) The phase II response, however, decreased u(Cl)/u(Na) from 1.27 to 1.24, and the effect could be abrogated by lowering extracellular Ca2+. These results indicate that phase II decreases in G(T) across cultured human cervical epithelium are mediated by acute decreases in tight-junctional permeability.