Ca2+ influx gated by inositol-3,4,5,6-tetrakisphosphate in NIH/3T3 fibroblasts.

The functional role of three inositol tetrakisphosphate isomers on Ca2+ influx was examined by intracellular application in NIH/3T3 mouse fibroblasts. Infusion of inositol-1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4), inositol-1,3,4,6- tetrakisphosphate, and inositol-3,4,5,6-tetrakisphosphate (Ins(3,4,5,6)P4) from the patch pipette into the cytoplasm produced a transient increase in cytoplasmic free Ca2+ concentration by fura-2 recording in extracellular Ca(2+)-dependent fashion. Stimulation of NIH/3T3 cells with bradykinin increased the levels of Ins(1,3,4,5)P4 and Ins(3,4,5,6)P4. These results suggest that mouse fibroblast cells possess a Ca2+ influx pathway gated with naturally occurring inositol tetrakisphosphates in response to stimulation with bradykinin.