Sulfhydryl groups of renal D1A dopamine receptors: differential sensitivity of receptors to N-ethylmaleimide in normotensive and hypertensive rats.

OBJECTIVES

To determine whether sulfhydryl groups are present on D1A receptors of spontaneously hypertensive rats (SHR) and to test the hypothesis that failure of agonists to bind to such receptors is linked to microstructural changes involving sulfhydryl groups.

METHOD

Alkylation of renal proximal tubule membranes by N-ethylmaleimide caused 70% loss of D1A dopamine receptor binding sites in the normotensive Wistar-Kyoto (WKY) rat and the SHR.

RESULTS

The concentration of N-ethylmaleimide (IC50) required to produce half-maximal loss of receptor binding was 5.2 and 1200 mumol/l in WKY rats and SHR, respectively. Previous receptor occupancy of WKY rat D1A sites by the D1A agonist SKF R-38393 completely protected the binding sites from N-ethylmaleimide-mediated inactivation. Occupancy with the D1A antagonist SCH 23390 partially protected the binding sites and produced a 500-fold increase in the IC50 of N-ethylmaleimide. In SHR, receptor occupancy either by SKF R-38393 or by SCH 23390 failed to protect the D1A sites from N-ethylmaleimide or to alter the IC50 of N-ethylmaleimide-mediated inactivation.

CONCLUSION

These results indicate that D1A dopamine receptors both of WKY rats and of SHR contain sulfhydryl groups at or near the ligand binding site, which display differential sensitivity to N-ethylmaleimide.