Role of membrane sulfhydryl groups in stimulation of renin secretion by sulfhydryl reagents.

The present study was designed to address the reactivity and accessibility of the particular class of sulfhydryl groups involved in the regulatory process of renin secretion. Both mercurial (such as P-chloromercuriphenyl sulfonate [PCMPS] and non-mercurial sulfhydryl reagents (for example, 6,6-dithiodinicotinic acid [DTDN]), which very slowly penetrate the cell membrane of intact cells, stimulated renin secretion. The membrane permeant sulfhydryl reagent N-ethylmaleimide had no effect on renin secretion but its membrane impermeant derivative, stilbene maleimide, strongly stimulated secretion. Furthermore, disulfide reducing agents such as dithiothreitol (DTT) had no effect on renin secretion at low concentrations, but strongly inhibited it at high concentrations. Several reagents which are known to primarily deplete cellular reduced glutathione were without effect on renin secretion. The stimulation of renin secretion by PCMPS was rapid in onset, and prevented and reversed by DTT and L-cysteine. Furthermore, the maximal stimulatory effect of PCMPS was not additive to that by diuretics with sulfhydryl reactivity (such as, ethacrynic acid and mersalyl). The stimulatory effect of PCMPS was not affected by diuretics which lack sulfhydryl reactivity (such as, bumetanide and furosemide). These results suggest that sulfhydryl reagents of both with and without diuretic activity stimulate renin secretion by reacting with specific class of sulfhydryl groups which are readily accessible from the extracellular compartment. In addition, these results provide further support the possibility that a sulfhydryl-disulfide interchange in the membrane may play a regulatory role in the renin secretory process.

Cellular mechanism of stimulation of renin secretion by the mercurial diuretic mersalyl.

The aim of the present study was to elucidate the cellular mechanism by which the mercurial diuretic mersalyl stimulates renin secretion in rabbit renal cortical slices in vitro. The stimulatory effect of mersalyl on renin secretion was rapid, reversible and concentration dependent. The stimulation was not dependent on the presence of ions such as Na+, Cl- and Ca++, and it was unaffected by inhibitors of Na+/K+/2Cl- cotransport, such as bumetanide and furosemide. However, the stimulation was blocked and reversed by thiols, such as L-cysteine and dithiothreitol. Furthermore, the maximal stimulatory effect of mersalyl on renin secretion was not additive to that produced by the non-diuretic mercurial sulfhydryl reagent P-chloromercuriphenylsulfonate nor to that produced by the non-mercurial diuretic sulfhydryl reagent, ethacrynic acid. These results support the hypothesis that mersalyl stimulates renin secretion by forming a reversible mercaptide bond with sulfhydryl groups, located perhaps on the plasma membrane of juxtaglomerular cells. These particular sulfhydryl groups appear to have no functional role in the diuretic action of mersalyl.

Stimulation of renin secretion by ethacrynic acid is independent of Na(+)-K(+)-2Cl- cotransport.

This study investigated the cellular mechanism of stimulation of renin secretion by the loop diuretic ethacrynic acid (EA) in rabbit renal cortical slices. The diuretic rapidly stimulated renin secretion reversibly and in a concentration-dependent manner. The stimulation was independent of the presence of Na+, Cl-, Ca2+, or other loop diuretics (furosemide and bumetanide) in the incubation media, suggesting that the stimulation in vitro was not dependent on the inhibitory effect of the diuretic on Na(+)-K(+)-2Cl-cotransport. The findings do not support the macula densa hypothesis. The stimulation by the diuretic was prevented and reversed by thiols such as cysteine and dithiothreitol, which also prevented and reversed the stimulation of renin secretion by the nondiuretic sulfhydryl reagent P-chloromercuriphenyl-sulfonate (PCMPS). These results suggest that EA stimulates renin secretion in vitro via reversible chemical reactions with specific membrane sulfhydryl groups that may have no functional role in the Na(+)-K(+)-2Cl- cotransport.