Effects of kinins upon cytosolic calcium concentrations in mouse mesangial cells

Abstract

Bradykinin (BK) induces increases in cytosolic calcium concentration [Ca++]i in several cell lines. Because the role of BK in the renal system, particularly in mesangial cell (MC), is not clear, we investigated the effects of kinins on [Ca++]i in mouse-immortalized MC. [Ca++]i was evaluated by spectrofluorometry and expressed as a ratio between the obtained and basal [Ca++]i. BK (0.1 μM) induced a non-sustained increase in [Ca++]i (4.70±0.27; N=28). A similar effect was observed with the B2 receptor agonist, Tyr8-BK (0.1 μM, 3.34±0.48; N=7), while B1 receptor agonists, des-Arg10-Kallidin (Kal) (1 μM, N=11) and des-Arg9-BK (1 μM, N=8), exhibited only discrete responses (1.45±0.08 and 1.12±0.04, respectively). Cross-desensitization was seen between BK and Tyr8-BK, but not between BK and des-Arg10-Kal. The BK response was decreased (5.09±0.30, N=6 to 1.57±0.12, N=7, P<0.001) by the B2 receptor antagonist HOE 140 (0.1 μM, 15 min), while the B1 receptor antagonist des-Arg9-[Leu8]-BK (1 μM, 15 min) had no effect on BK or des-Arg10-Kal actions. Incubation of cells with Escherichia coli lipopolysaccharide (100 μg/ml, 24 h) alone or in association with tumor necrosis factor-α (TNF-α) (10 ng/ml, N=6) did not enhance B1 agonist responses. BK was inhibited by repeated cell washouts in zero Ca++ solution (2.04±0.19, N=6 P<0.001), and the residual response was almost abolished by thapsigargin (Thaps) a sarcoplasmic reticulum (SR) calcium-ATPase inhibitor (1 μM) (1.18±0.08, N=5 P<0.001). Additionally, BK was not inhibited by verapamil (50 μM), nifedipine (30 μM), Ni++ (300 μM) or La+++ (10 μM). In conclusion, BK induces [Ca++]i in mouse MC mainly by B2 receptor activation. B1 receptors have a minor role in this phenomenon even in the presence of known B1 receptor synthesis inducers. Finally, BK mobilizes extracellular calcium sources and, to a lesser extent, intracellular Thaps-sensitive calcium stores. The ion channels involved in calcium influx remain to be detected.