Protein kinase C contributes to desensitization of ANG II signaling in adult rat cardiac fibroblasts.
We have studied G(q)-linked ANG II signaling [inositol phosphate (IP) accumulation, Ca(2+) mobilization] in primary cultures of rat cardiac fibroblasts (CFs) and have found that ANG II initiates a protein kinase C (PKC)-mediated negative feedback loop that rapidly terminates the ANG II response. Pharmacological inhibition of PKC by staurosporine and GF-109203X doubled IP production over that achieved in response to ANG II alone. Inhibition of PKC also led to larger Ca(2+) transients in response to ANG II, suggesting that Ca(2+) mobilization was proportional to G(q)-phospholipase C-IP(3) activity under the conditions studied. Depletion of cellular PKC by overnight treatment with phorbol 12-myristate 13-acetate (PMA) similarly augmented ANG II-induced IP production. Acute activation of PKC by PMA halved IP formation, with an EC(50) approximately 1 nM; 4alpha-PMA was inactive. Time course data demonstrated that ANG II-mediated IP production fully desensitized within 30 s; PKC inhibition reduced the rate and extent of this desensitization. In cells desensitized to ANG II, a purinergic agonist still mobilized intracellular Ca(2+), indicating that desensitization was homologous. The ANG II-induced Ca(2+) signal was fully resensitized within 30 min. The data demonstrate that a large portion of the IP-Ca(2+) responses of rat CFs to ANG II are short-lived because of rapid, PKC-mediated desensitization.
Meszaros
J G
JG
Department of Pharmacology, University of California, San Diego, School of Medicine, La Jolla, California 92093-0636, USA.
Raphael
R
R
Lio
F M
FM
Brunton
L L
LL
D000367:Age Factors; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D002021:Buffers; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D005347:Fibroblasts / Q000737:chemistry / Q000166:cytology / Q000201:enzymology; D007295:Inositol Phosphates / Q000378:metabolism; D008297:Male; D009206:Myocardium / Q000737:chemistry / Q000166:cytology* / Q000201:enzymology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D011945:Receptors, Angiotensin / Q000378:metabolism; D011983:Receptors, Purinergic / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014544:Uridine Triphosphate / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology*
D002021:Buffers; D002614:Chelating Agents; D007295:Inositol Phosphates; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D011945:Receptors, Angiotensin; D011983:Receptors, Purinergic; D014662:Vasoconstrictor Agents; D000804:Angiotensin II; D004533:Egtazic Acid; D011493:Protein Kinase C; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium; D014544:Uridine Triphosphate