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 m anner that is characterized by a rapid increase (phase I) followed by a sustained decrease in GT (phase II). We tested the hypothesis that t he phase II response is mediated by decreases in the permeability of t ight junctions. We studied the effect of ATP on the relative mobilitie s of Cl- vs. Na+ (u(Cl)/u(Na)) as calculated from changes in the dilut ion potential (V-dil). V-dil was induced by lowering NaCl from 130 to 10 mM in either the luminal or subluminal solutions bathing filters co ntaining 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 hypertoni c gradients (which increase permeability of lateral intercellular spac e) 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 resistanc e. 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 respo nse, however, decreased u(Cl)/u(Na) from 1.27 to 1.24, and the effect could be abrogated by lowering extracellular Ca2+. These results indic ate that phase II decreases in G(T) across cultured human cervical epi thelium are mediated by acute decreases in tight-junctional permeabili ty.