| Abstract: | The addition of bradykinin to NG115-401L cells grown on coverslips results in the generation of rapid transient increases in intracellular Ca2+] and inositol phosphates. Changes in intracellular Ca2+, measured using the fluorescent indicator dye Fura-2, show two components; an initial rapid peak in Ca2+]i which is essentially independent of extracellular Ca2+, and a sustained plateau dependent on the presence of extracellular Ca2+. Analysis of bradykinin stimulated production of 3H]inositol phosphates, by h.p.l.c., shows a rapid biphasic production of inositol 1,4,5-trisphosphate, inositol tetrakisphosphate and inositol bisphosphates, followed by a sustained rise in inositol 1,3,4-trisphosphate production. Quantitative measurements have indicated the presence of other, more polar, 3H]inositol-labelled metabolites which do not show major changes on bradykinin stimulation. The initial phase of inositol phosphate production parallels the rapid transient increase in intracellular Ca2+], however, the second phase of inositol phosphate production occurs when intracellular Ca2+] is declining and implies a complex series of regulatory events following receptor stimulation. Similar time courses of inositol 1,4,5-trisphosphate and Ca2+ signals provides supporting evidence that inositol 1,4,5-trisphosphate is the second messenger coupling bradykinin receptor stimulation to release of Ca2+ from intracellular stores. |
