Protein kinase C-mediated inhibition of renal Ca2+ ATPase by physiological concentrations of angiotensin II is reversed by AT1- and AT2-receptor antagonists.
Angiotensin II (Ang II) increases the cytosolic Ca2+ concentration in different cell types. In this study, we investigate the effect of Ang II on the Ca2+ ATPase of purified basolateral membranes of kidney proximal tubules. This enzyme pumps Ca2+ out of the cytosol in a reaction coupled to ATP hydrolysis, and it is responsible for the fine-tuned regulation of cytosolic Ca2+ activity. Ca2+-ATPase activity is inhibited by picomolar concentrations of Ang II, with maximal inhibition being attained at approximately 50% of the control values. The presence of raising concentrations (10(-11) to 10(-7) M) of losartan (an AT1-receptor antagonist) or PD123319 (an AT2-receptor antagonist) gradually reverts inhibition by Ang II. Both the phospholipase C (PLC) inhibitor U-73122 (10(-6) M) and the inhibitor of protein kinase C (PKC) staurosporine (10(-7) M) prevent inhibition of the Ca2+ pump by Ang II. Incubation of the previously isolated membranes with a PKC activator-the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (10(-8) M)-mimics the inhibition found with Ang II, and the effects of the compounds are not additive. Taken as a whole, these results indicate the Ang II inhibits Ca2+-ATPase by activation of a PKC system present in primed state in these membranes after binding of the hormone to losartan- and PD123319-sensitive receptors coupled to a PLC. Therefore, inhibition of the basolateral membrane Ca2+-ATPase by kinase-mediated phosphorylation appears to be one of the pathways by which Ang II promotes an increase in the cytosolic Ca2+ concentration of proximal tubule cells.
Assunção-Miranda
Iranaia
I
Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro 21941-590, Rio de Janeiro, Brazil.
Guilherme
Adilson L
AL
Reis-Silva
Clédson
C
Costa-Sarmento
Glória
G
Oliveira
Mécia M
MM
Vieyra
Adalberto
A
D000804:Angiotensin II / Q000494:pharmacology*; D047228:Angiotensin II Type 1 Receptor Blockers / Q000494:pharmacology*; D057912:Angiotensin II Type 2 Receptor Blockers; D000818:Animals; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D007093:Imidazoles / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D019808:Losartan / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism*; D044139:Receptor, Angiotensin, Type 2 / Q000378:metabolism; D012756:Sheep; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D047228:Angiotensin II Type 1 Receptor Blockers; D057912:Angiotensin II Type 2 Receptor Blockers; D007093:Imidazoles; D011725:Pyridines; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D014662:Vasoconstrictor Agents; D000804:Angiotensin II; C073402:PD 123319; D011493:Protein Kinase C; D000252:Calcium-Transporting ATPases; D019808:Losartan