AJP - Cell Physiology, Vol 246, Issue 3 242-C246, Copyright © 1984 by American Physiological Society

ARTICLES

Sensitivity of cAMP-stimulated salt secretion in shark rectal gland to "loop" diuretics

H. C. Palfrey, P. Silva and F. H. Epstein

The secretory response of isolated perfused shark rectal gland was characterized with respect to its inhibition by a chemically related series of 5-sulfamoylbenzoic acid derivatives and certain phenoxyacetic acid derivatives. Maximal fluid and salt secretion was elicited with dibutyryl adenosine 3',5'-cyclic monophosphate and theophylline. The potency series established for the 5-sulfamoylbenzoic acid compounds agreed well with the relative potencies previously established for these agents as inhibitors of Na+-K+-Cl- cotransport in the avian erythrocyte. The most potent compound tested (3-benzylamino-4-phenyl-5-sulfamoylbenzoic acid) had a 50% inhibitory concentration value of approximately 5 X 10(-7) M. This compound was approximately 10-fold more effective than bumetanide and 400-fold as inhibitory as furosemide in this system. Ethacrynic acid (EA; 10(-3) M) was a poor inhibitor of rectal gland secretion and was approximately equipotent with its saturated derivative, dihydro EA. In contrast, EA-L-cysteine was fully effective at 10(-4) M, although the EA-D-cysteine adduct was ineffective. These data also qualitatively agree with results obtained in the inhibition of avian erythrocyte Na+-K+-Cl- cotransport and suggest that the rectal gland possesses a serosally oriented "NaCl cotransport" system with pharmacological and perhaps physiological similarities to the Na+-K+-Cl-cotransporter found in erythrocyte and other cell membranes.

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