DUAL ROLE FOR ALF4--SENSITIVE G-PROTEINS IN THE FUNCTION OF T84 EPITHELIAL-CELLS - TRANSPORT AND BARRIER EFFECTS

T84 monolayers were studied to determine the effect of AlF4-, an activ ator of heterotrimeric G proteins, on Cl- secretion and intestinal bar rier function. Basolateral (but not apical) addition of AlF4- increase d short-circuit current (I-sc) and decreased transepithelial resistanc e. Preincubation with the heavy metal chelator deferoxamine showed tha t both effects were dependent on Al3+. The effect on I-sc was abolishe d by the intracellular Ca2+ chelator 1,2-bis(2-aminophenoxy) ethane-N, N,N',N'-tetraacetic acid or in Cl--free solutions, whereas the decreas e in resistance was unaffected. AlF4- also increased intracellular Ca2 +, as assessed via fura 2 fluorometry. AlF4- had no effect on adenosin e 3',5'-cyclic monophos phate (cAMP) or guanosine 3',5'-cyclic monopho sphate (cGMP) levels in T84 cells. The effect of AlF4- on transepithel ial resistance was accompanied by a decrease in cellular F-actin as we ll as increased transepithelial fluxes of the paracellular markers man nitol and inulin. The results indicate that AlF4--sensitive G proteins regulate both epithelial secretory and barrier functions, but via dif ferent pathways. AlF4-, increases Cl- secretion via a Ca2+-dependent a nd cAMP- and cGMP-independent mechanism in T84 cells, whereas the decr ease in resistance is independent of Ca2+.