Role of protein kinase-C in the alpha 1-adrenoceptor-mediated responses of perfused rat liver.
The present work aimed to determine the role played by protein kinase-C (PKC) in the alpha 1-adrenoceptor-induced activation of hepatic metabolism. The following observations indicate that activation of PKC is a condition necessary for alpha 1-adrenoceptor activation of hepatic functions, but not sufficient to mimic the receptor-mediated effects in the absence of external physiological stimuli. 1) alpha 1-Adrenoceptor activation promoted the translocation of PKC from the cytosol to its active form in the plasma membrane. 2) Activation of PKC by the phorbol ester 12-myristate 13-acetate or exogenous diacylglycerols or by elevation of endogenous levels of diacylglycerols by inhibiting diacylglycerol kinase mimicked the alpha 1-adrenoceptor-mediated actions. However, the time course and magnitude of the nonreceptor responses differ from those mediated by alpha 1-adrenoceptor activation. In addition, nonreceptor-mediated activation of PKC decreased the alpha 1-adrenoceptor responsiveness. 3) Inhibition of PKC by either H-7 [1-(5-isoquinolinilsulfonyl)2-methylpiperazine] or staurosporine inhibited all of the alpha 1-adrenoceptor-induced responses, except gluconeogenesis. The vasopressin effects were not inhibited by H-7, indicating that PKC activation is a distinct feature of the hepatic alpha 1-adrenoceptor activation that is not shared by all the Ca(2+)-mobilizing agonists. The diacylglycerol-PKC branch of the alpha 1-adrenoceptor signaling pathway seems to control the sustained phase of stimulation of hepatic functions. In these studies we have also observed that phorbol 12-myristate 13-acetate produces a concentration-dependent inhibition of hepatic respiration. However, decreased energy availability does not seem to be the cause of its action to decrease alpha 1-adrenoceptor responsiveness.
Urcelay
E
E
Endocrine Physiology Unit, Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain.
Butta
N
N
Manchón
C G
CG
Ciprés
G
G
Requero
A M
AM
Ayuso
M S
MS
Parrilla
R
R
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000201:enzymology; D003600:Cytosol / Q000201:enzymology; D004075:Diglycerides / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D007546:Isoquinolines / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000502:physiology*; D008297:Male; D010477:Perfusion; D010879:Piperazines / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D000470:Alkaloids; D004075:Diglycerides; D007546:Isoquinolines; D010879:Piperazines; D011942:Receptors, Adrenergic, alpha; C044295:1,2-dioctanoylglycerol; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D011493:Protein Kinase C; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate