endothelin-1 and adenosine-3--5--cyclic-phosphorothioate

Previous studies have shown that endothelin (ET) antagonizes the actions of arginine vasopressin (AVP) in the renal collecting ducts. On the other hand, the effects of AVP on ET function within the collecting ducts of the kidney have not been investigated extensively. Using isolated inner medullary collecting ducts (IMCD), we examined the possibility that a decrease in ET(B) receptor mRNA accompanied AVP-induced downregulation of ET(B) receptors. Binding studies revealed that overnight incubation of rat IMCD cells with AVP significantly reduced the maximal binding capacity (B(max)) of ET. Activation of adenylate cyclase by forskolin decreased the total ET(B) receptor density by approximately 42% but did not affect the density of ET(A) receptors. The Rp diastereoisomer of adenosine 3', 5'-cyclic monophosphothionate, Rp-cAMPS (a specific inhibitor of protein kinase A), blocked the AVP-induced reduction in ET receptor density. Using competitive PCR method, we also observed downregulation of ET(B) receptor mRNA in IMCD treated with AVP. Additional studies were done with IMCD to determine whether AVP inhibited the ET-induced accumulation of cGMP. We saw a reduction in ET-induced cGMP accumulation when IMCD was incubated overnight with AVP. This inhibition of ET-induced accumulation of cGMP was blocked by Rp-cAMPS. These results suggest that AVP regulates ET(B) receptor expression in IMCD.

Topics: Animals; Arginine Vasopressin; Colforsin; Cyclic AMP; Cyclic GMP; Endothelin-1; Kidney Medulla; Kidney Tubules, Collecting; Male; Rats; Rats, Wistar; Receptor, Endothelin B; Receptors, Endothelin; RNA, Messenger; Thionucleotides; Time Factors; Vasopressins

The role of cAMP and cAMP-dependent protein kinase A (PKA) in endothelin (ET)-stimulated migration of human neutrophils was studied. Endothelins caused an increase in neutrophil migration when they were applied in low (nanomolar) concentrations; stimulation of migration was either predominantly chemokinetic (ET-1) or chemotactic (ET-2, ET-3). All endothelins, at concentrations which gave maximal stimulation of migration, caused an increase of cAMP level. Two inhibitors of adenylate cyclase, MDL-12330A and SQ-22536, completely inhibited migration activated by ET-1, ET-2 or ET-3, indicating that cAMP generation played a decisive role in endothelin-activated migration. The role of PKA in endothelin-activated migration was considered. Two specific antagonists of PKA strongly inhibited endothelin-activated migration. KT-5720, an inhibitor of PKA, also inhibited ET-activated migration, but only when electroporated cells were used. The results suggest that the effect of cAMP on endothelin-activated migration was mediated by PKA.

Topics: Adenine; Adenylyl Cyclase Inhibitors; Carbazoles; Cell Movement; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Endothelin-1; Endothelin-2; Endothelin-3; Endothelins; Enzyme Inhibitors; Humans; Imines; Indoles; Neutrophils; Pyrroles; Thionucleotides

The mechanism of endothelin-1 (ET-1)-induced atrial natriuretic peptide (ANP) release was studied in neonatal rat ventricular cardiomyocytes. These cells expressed a single high-affinity class of ETA receptor (dissociation constant = 54 +/- 18 pM, n = 3), but no ETB receptors. Incubation of cardiomyocytes with ET-1 led to concentration-dependent ANP release and prostacyclin production. ET-1-induced ANP release was affected by neither protein kinase C (PKC) inhibition or downregulation nor by cyclooxygenase inhibition, indicating that ET-1-stimulated ANP secretion is not a PKC-mediated, prostaglandin-dependent process. Furthermore, ET-1 significantly stimulated adenosine 3',5'-cyclic monophosphate (cAMP) production and increased cytosolic calcium concentration in these preparations. Both ET-1-induced calcium influx and ANP release were decreased by the cAMP antagonist Rp-cAMPS, the Rp diastereoisomer of cAMP. Moreover, ET-1-induced ANP secretion was strongly inhibited in the presence of nifedipine as well as in the absence of extracellular calcium. Thus our results suggest that ET-1 stimulates ANP release in ventricular cardiomyocytes via an ETA receptor-mediated pathway involving cAMP formation and activation of a nifedipine-sensitive calcium channel.

Topics: Alkaloids; Animals; Animals, Newborn; Atrial Natriuretic Factor; Benzophenanthridines; Calcium; Cells, Cultured; Cyclic AMP; Cyclooxygenase Inhibitors; Egtazic Acid; Endothelin-1; Enzyme Inhibitors; Epoprostenol; Heart; Heart Ventricles; Kinetics; Myocardium; Naphthalenes; Nifedipine; Phenanthridines; Protein Kinase C; Rats; Rats, Wistar; Receptor, Endothelin A; Receptor, Endothelin B; Receptors, Endothelin; Staurosporine; Thionucleotides