The effect of big endothelin-1 in the proximal tubule of the rat kidney.
1. An obligatory step in the biosynthesis of endothelin-1 (ET-1) is the conversion of its inactive precursor, big ET-1, into the mature form by the action of specific, phosphoramidon-sensitive, endothelin converting enzyme(s) (ECE). Disparate effects of big ET-1 and ET-1 on renal tubule function suggest that big ET-1 might directly influence renal tubule function. Therefore, the role of the enzymatic conversion of big ET-1 into ET-1 in eliciting the functional response (generation of 1,2-diacylglycerol) to big ET-1 was studied in the rat proximal tubules. 2. In renal cortical slices incubated with big ET-1, pretreatment with phosphoramidon (an ECE inhibitor) reduced tissue immunoreactive ET-1 to a level similar to that of cortical tissue not exposed to big ET-1. This confirms the presence and effectiveness of ECE inhibition by phosphoramidon. 3. In freshly isolated proximal tubule cells, big ET-1 stimulated the generation of 1,2-diacylglycerol (DAG) in a time- and dose-dependent manner. Neither phosphoramidon nor chymostatin, a chymase inhibitor, influenced the generation of DAG evoked by big ET-1. 4. Big ET-1-dependent synthesis of DAG was found in the brush-border membrane. It was unaffected by BQ123, an ETA receptor antagonist, but was blocked by bosentan, an ETA.B-nonselective endothelin receptor antagonist. 5. These results suggest that the proximal tubule is a site for the direct effect of big ET-1 in the rat kidney. The effect of big ET-1 is confined to the brush-border membrane of the proximal tubule, which may be the site of big ET-1 sensitive receptors.
Beara-Lasić
L
L
Department of Physiology, Zagreb University School of Medicine, Croatia.
Knotek
M
M
Cejvan
K
K
Jaksić
O
O
Lasić
Z
Z
Skorić
B
B
Brkljacić
V
V
Banfić
H
H
D000818:Animals; D000077300:Bosentan; D002478:Cells, Cultured; D004075:Diglycerides / Q000096:biosynthesis*; D004305:Dose-Response Relationship, Drug; D019332:Endothelin-1; D016232:Endothelins / Q000494:pharmacology*; D006020:Glycopeptides / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008871:Microvilli / Q000187:drug effects; D011498:Protein Precursors / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D017466:Receptors, Endothelin / Q000819:agonists*; D013449:Sulfonamides / Q000494:pharmacology
D004075:Diglycerides; D019332:Endothelin-1; D016232:Endothelins; D006020:Glycopeptides; D011498:Protein Precursors; D017466:Receptors, Endothelin; D013449:Sulfonamides; D000077300:Bosentan; C008890:phosphoramidon