Modulation by neuropeptides of bradykinin-stimulated second messenger release in dorsal root ganglion neurons

Abstract

Fetal rat dorsal root ganglion neurons (7–8 days in culture) were labeled with [3H]arachidonic acid for 24 h. Stimulation with 10 μM bradykinin (BK) for 30 s resulted in nearly 2-fold increases in levels of radioactive diglyceride and arachidonic acid. A similar result was obtained in the absence of receptor stimulation using the Ca2+ channel agonist BAY K 8644 (10 μM, in the presence of 100 mM potassium chloride) or the Ca2+ ionophore, ionomycin (2.5 μM). If Ca2+ influx was inhibited by adding 3 mM Co2+, a blocker of voltage-sensitive calcium channels, or 2.5 mM EDTA, then BK-stimulated accumulation of both arachidonate and diglyceride was inhibited. These data suggest Ca2+ influx is required for ligand-stimulated accumulation of both arachidonate (a product of diglyceride-lipase or phospholipase A2) and diglyceride (a product of phospholipase C). Two distinct populations of channels may be involved in these reactions since pretreatment with 10 μM nifedipine or 50 μM verapamil (agents which block a subset of voltage-sensitive Ca2+ channels) inhibited BK-stimulated accumulation of arachidonic acid, but did not inhibit diglyceride accumulation. Such functional discrimination appears to have physiological importance; the inhibitory effect of nifedipine and verapamil on BK-stimulated arachidonate release was mimicked by pretreatment with peptides which decrease Ca2+ channel conductance in dorsal root ganglion neurons. The three peptides used were 1 μM neuropeptide Y, 10 μM somatostatin, and 10 μM[N-MePhe3,d-Pro4]-morphiceptin. The effect of neuropeptide Y was blocked by pretreatment with pertussis toxin. We conclude that ligand-stimulated arachidonic acid release may be blocked by occupation of inhibitory peptide sites coupled to a subset of calcium channels by a pertussis toxin sensitive G-protein.