Nitric oxide alters cytosolic potassium in cultured glomerular mesangial cells

Endothelium-derived relaxing factor is believed to be nitric oxide (NO). Evidence suggests that it has important functions in the regulation of mesangial cell (MC) tone and possibly in inflammation. As a vasodilator, its vasorelaxant effect depends, in part, on changes in cell membrane potential. We therefore tested the hypothesis that MCs in culture produce NO that results in cell relaxation through the opening of K+ conductance pathways. The K(+)-sensitive fluorescent dye, potassium-binding benzofuran isophthalate, was used to detect rapid changes in intracellular K+ concentration ([K+]i). The membrane potential-sensitive dye, 1,3-(sulfonatopropyl)-4-([beta-di-n- butylamino)-6-naphthyl]vinyl)pyridinium betaine (Di-4-AN-EPPS), was used to detect changes in membrane potential. Basal [K+]i was 92 +/- 9 mM (n = 46). In response to sodium nitroprusside (SNP), acetylcholine (ACh), and bradykinin (BK), [K+]i decreased to 72 +/- 7 (n = 5, P < 0.05), 70 +/- 8 (n = 7, P < 0.05), and to 69 +/- 13 mM (n = 6, P < 0.05), respectively. [K+]i rapidly returned to basal level in the continued presence of all three agonists. The SNP-, ACh-, and BK-induced decrease in [K+]i was significantly blunted by Ba2+ by 85, 92, and 89%, respectively (n > 4 for each agonist examined, P < 0.0001). NG-monomethyl-L-arginine (L-NMMA) and methylene blue inhibited the [K+]i-lowering effect of ACh and BK by 94 and 85% for L-NMMA (n = 5 for each agonist, P < 0.0001) and by 67 and 72% for methylene blue (n = 5 for each agonist, P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)