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 mu M) induced a non-sustained increase in [Ca++](i) (4.70 +/- 0.27; N = 28). A similar effect was observed with the B-2 receptor agonist, Tyr(8)-BK (0.1 mu M, 3.34 +/- 0.48; N = 7), while B-1 receptor agonists, des-Arg(10)-Kal-lidin (Kal) (1 mu M, N = 11) and des-Arg(9)-BK (1 mu M, N = 8), exhibited only discrete responses (1.45 +/- 0.08 and 1.12 +/- 0.04, respectively). Cross-desensitization was seen between BK and Tyr(8)-BK, but not between BK and des-Arg(10)-Kal. the BK response was decreased (5.09 +/- 0.30, N = 6 to 1.57 +/- 0.12, N = 7, P < 0.001) by the B-2 receptor antagonist HOE 140 (0.1 mu M, 15 min), while the B-1 receptor antagonist des-Arg(9)-[Leu(8)]-BK (1 mu M, 15 min) had no effect on BK or des-Arg(10)-Kal actions. Incubation of cells with Escherichia coli lipopolysaccharide (100 mu g/ml, 24 h) alone or in association with tumor necrosis factor-alpha (TNF-alpha) (10 ng/ml, N = 6) did not enhance B-1 agonist responses. BK was inhibited by repeated cell washouts in zero Ca++ solution (2.04 +/- 0.19, N = 6 r < 0.001), and the residual response was almost abolished by thapsigargin (Thaps) a sarcoplasmic reticulum (SR) calcium-ATPase inhibitor (1 mu M) (1.18 +/- 0.08, N = 5 P < 0.001). Additionally, BK was not inhibited by verapamil (50 mu M), nifedipine (30 mu M), Ni++ (300 mu M) or La+++ (10 mu M). in conclusion, BK induces [Ca++](i) in mouse MC mainly by B-2 receptor activation. B-1 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. (C) 1999 Elsevier Science B.W. All rights reserved.