Biliary lactoferrin concentrations are increased in active inflammatory bowel disease: a factor in the pathogenesis of primary sclerosing cholangitis?

We have used the whole-cell patch-clamp technique to study the effects of inositol 1,4,5,6-tetrakisphosphate [Ins(1,4,5,6)P4], inositol 3,4,5,6-tetrakisphosphate [Ins(3,4,5,6)P4] and inositol 1,3, 4,5,6-pentacisphosphate [Ins(1,3,4,5,6)P5] on volume-activated Cl- currents (ICl,vol) in cultured endothelial cells from bovine pulmonary artery (CPAE cells). Ins(1,4,5,6)P4 and Ins(3,4,5,6)P4 were applied intracellularly via the patch pipette at concentrations between 10 and 100 muM. Both tetrakisphosphates inhibited the Cl- current ICl,Ca, which was activated by intracellular loading of the cells with 500 nM Ca2+ [for inhibition by Ins(1,4,5,6)P4: 58% at 10 muM, 75% at 100 muM; for Ins(3,4,5,6)P4: 44% at 10 muM, 65% at 100 muM]. Inhibition of ICl,Ca occurred without significant changes in its kinetic properties. The amplitude of ICl,vol activated by a 13.5 or 27% hypotonic solution at +100 mV was strongly reduced in cells loaded with either tetrakisphosphate, i.e. a 73% reduction for Ins(3,4,5,6)P4 and 89% for Ins(1,4,5,6)P4 at 100 muM. Both tetrakisphosphates also inhibited a current probably identical to ICl,vol which was activated by dialysing the cell with 100 muM guanosine 5'-O-(3-thiotriphosphate) (GTP[gamma-S]). Ins(1, 3,4,5,6)P5 at a concentration of 30 muM did not significantly reduce ICl, vol. The effects of Ins(3,4,5,6)P4 may represent an inhibitory pathway for the ICl,Ca and ICl,vol in macrovascular endothelium after sustained receptor-mediated activation of phospholipase C.