BRADYKININ (BK) INCREASES CYTOSOLIC CALCIUM IN CULTURED RAT MYENTERIC NEURONS VIA BK-2 TYPE RECEPTORS COUPLED TO MOBILIZATION OF EXTRACELLULAR AND INTRACELLULAR SOURCES OF CALCIUM - EVIDENCE THAT CALCIUM INFLUX IS PROSTAGLANDIN DEPENDENT

We examined the effect of bradykinin (Bk) on cytosolic calcium ([Ca++](i)) in cultured rat ileal myenteric neurons. The receptor subtype(s) and calcium pool(s), e.g., extracellular and/or intracellular calcium that mediate Bk's effect on [Ca++](i) in myenteric neurons, have not been reported. Superfusion with Bk (10 nM) increased [Ca++](i) by 96 +/- 10 nM over basal levels in similar to 80% of the neurons tested that were not affected by a Bk-1 receptor antagonist but were inhibited 72% by a Bk-2 receptor antagonist. The Bk-generated increase in [Ca++](i) was reduced by 45% and 52% of control response in calcium-free buffer and indomethacin, respectively, supporting involvement of extracellular and intracellular pools of calcium and mediation, in part, by a prostaglandin-dependent pathway. Bk increased [Ca++](i) by 54 +/- 6 nM in calcium-free buffer that was indomethacin insensitive, suggesting that Bk stimulation of extracellular calcium influx was mediated by a prostaglandin-dependent pathway. Bk (1 mu M) increased tissue prostaglandin E(2) (PGE(2)) production by 62% over basal levels in isolated rat ileal myenteric ganglia. Finally, superfusion with PGE(2) (10 mu M) increased [Ca++](i) by 105 +/- 16 nM over basal levels that were blocked in calcium-free buffer. In summary, our studies suggest that cultured rat ileal myenteric neurons express the Bk-2 receptor subtype that is coupled to mobilization of extracellular and intracellular pools of calcium. Bk stimulates influx of extracellular calcium via a prostaglandin-dependent pathway.