Characterization of atrial natriuretic factor receptors in human glomerular epithelial and mesangial cells
Chansel, D.; Pham, P.; Nivez, M.P.; Ardaillou, R.
American Journal of Physiology 259(4 Pt 2): F619-F627
1990
ISSN/ISBN: 0002-9513 PMID: 2171358 Document Number: 361614
To evaluate the distribution and functions of receptors of atrial natriuretic factor (ANF) in human glomeruli, we studied the binding sites of ANF-(1-28) in homogeneous populations of human glomerular epithelial cells or mesangial cells. 125I-labeled ANF bound specifically to both cell types. Equilibrium saturation binding curves suggested one group of receptor sites in mesangial cells (Kd = 99 .+-. 32 pmol/l, Bmax = 15.3 .+-. 3.5 fmol/mg) but multiple groups in glomerular epithelial cells. Binding was greater at 37 than at 4.degree. C in mesangial cells. The reverse was observed in glomerular epithelial cells due to marked degradation of the tracer at 37.degree. C. The fractions of undisplaceable tracer in a hypertonic acid medium after 60 min incubation were 45 and 16% at 37.degree. C for glomerular epithelial and mesangial cells, respectively. ANF-(1-28) and C-ANF-(4-23), a specific ligand of clearance receptors, similarly inhibited 125I-ANF binding to mesangial cells, whereas [Ala7-Ala23]-ANF, a linear analogue, was slightly less potent. In epithelial cells, C-ANF-(4-23) competitively inhibited 125I-ANF binding out with a lower potency than ANF, whereas linear ANF at low concentraitons (10-100 pmol/l) stimulated 125I-ANF binding. In addition, linear ANF markedly inhibited the degradation of 125I-ANF in the incubation medium of epithelial and mesangial cells, whereas thiorphan, an inhibitor of enkephalinase, was inactive. ANF-(1-28) stimulated cGMP production in glomerular epithelial cells but not in mesangial cells. Both analogues were inactive in both cell types and did not modify ANF-(1-28)-dependent cGMP synthesis. These results suggest the presence of a single type of ANF clearance receptors in human mesangial cells. In contrast, glomerular epithelial cells possess biological receptors linked to guanylate cyclase, clearance receptors, and also abundant membrane ectoenzymes able to degrade extracellular ANF, which are preferentially saturated by its linear analogue.