Abstract
Stimulation of the release of endothelium-derived relaxing factor (EDRF) in the kidney has been shown to result in natriuresis without affecting glomerular filtration rate. This may be due to EDRF directly regulating solute transport in the cortical collecting duct (CCD). To test this hypothesis, we measured the effect of bradykinin (Bk) or acetylcholine (Ach) on short-circuit current (Isc; a measure of active transport) in a CCD cell line (M-1), in the presence or absence of cow pulmonary artery endothelial (CPAE) cells. 10(-9) M Bk or 10(-7) M Ach had no effect on M-1 Isc in which CPAE cells were absent. The addition of CPAE cells to M-1 cells also did not affect M-1 Isc. On the other hand, when 10(-9) M Bk or 10(-7) M Ach were added to M-1 cells in the presence of CPAE cells, Isc decreased from 43 +/- 4.5 to 26 +/- 4 and 64 +/- 9 to 33 +/- 4 microA/cm2, respectively (P less than 0.001). Nitroarginine (N-Arg, 10(-4) M), a competitive inhibitor of EDRF production, blocked the inhibition in M-1 Isc due to both agonists. Since cGMP is the second messenger of EDRF in vascular smooth muscle, we measured the effects of Bk on cGMP production in M-1 cells in the presence and absence of CPAE cells. Bk increased cGMP content in M-1 cells in the presence of CPAE cells from 33 +/- 3.4 to 132 +/- 11.7 fmol/10(6) M-1 cells (P less than 0.001). When cultures of M-1 and CPAE cells were treated with N-Arg and challenged with Bk, Bk's effect on cGMP was partially blocked (61.4 +/- 12 fmol/10(-6) M-1 cells; NS). These data suggest that EDRF inhibits transport and increases cGMP content in M-1 cells.
Authors
B A Stoos, O A Carretero, R D Farhy, G Scicli, J L Garvin
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