INHIBITION BY INOSITOLTETRAKISPHOSPHATES OF CALCIUM-ACTIVATED AND VOLUME-ACTIVATED CL- CURRENTS IN MACROVASCULAR ENDOTHELIAL-CELLS

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)P-4], inositol 3,4 ,5,6-tetrakisphosphate [Ins(3,4,5,6)P-4] and inositol 1,3,4,5,6-pentac is-phosphate [Ins(1,3,4,5,6)P-5] on volume-activated Cl- currents (I-C l,I-vol) in cultured endothelial cells from bovine pulmonary artery (C PAE cells). Ins(1,4,5,6)P-4 and Ins(3,4,5,6)P-4 were applied intracell ularly via the patch pipette at concentrations between 10 and 100 mu M Both tetrakisphosphates inhibited the Cl- current I-Cl,I-Ca, which wa s activated by intracellular loading of the cells with 500 nM Ca2+ [fo r inhibition by Ins(1,4,5,6)P-4: 58% at 10 mu M, 75% at 100 mu M; for Ins(3,4,5,6)P-4: 44% at 10 mu M, 65% at 100 mu M] Inhibition of I-Cl,I -Ca occurred without significant changes in its kinetic properties. Th e amplitude of I-Cl,I-vol activated by a 13.5 or 27% hypotonic solutio n at +100 mV was strongly reduced in cells loaded with either tetrakis phosphate, i.e. a 73% reduction for Ins(3,4,5,6)P-4 and 89% for Ins(1, 4,5,6)P-4 at 100 mu M. Both tetrakisphosphates also inhibited a curren t probably identical to I-Cl,I-vol which was activated by dialysing th e cell with 100 mu M guanosine 5'-O-(3-thiotriphosphate) (GTP[gamma-g) . Ins(1,3,4,5,6)P-5 at a concentration of 30 mu M did not significantl y reduce I-Cl,I-vol. The effects of Ins(3,4,5,6)P-4 may represent an i nhibitory pathway for the I-Cl,I-Ca and I-Cl,I-vol in macrovascular en dothelium after sustained receptor-mediated activation of phospholipas e C.