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This version published online on November 18, 2004
Endocrinology, doi:10.1210/en.2004-1083
A more recent version of this article appeared on February 1, 2005
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Submitted on August 18, 2004
Accepted on November 8, 2004

{alpha}1A-Adrenoceptors activate glucose uptake in L6 muscle cells through a phospholipase C, phosphatidylinositol-3 kinase and atypical protein kinase C dependent pathway

Dana S. HUTCHINSON and Tore BENGTSSON*

Department of Physiology, The Wenner-Gren Institute, Arrhenius Laboratories F3, Stockholm University, SE 10691 Stockholm, Sweden

* To whom correspondence should be addressed. E-mail: Tore.Bengtsson{at}zoofys.su.se.

The role of {alpha}1-adrenoceptor activation on glucose uptake in L6 cells was investigated. The {alpha}1-adrenoceptor agonist phenylephrine (pEC50 5.27 ± 0.30) or cirazoline (pEC50 5.00 ± 0.23) increased glucose uptake in a concentration-dependent manner, as did insulin (pEC50 7.16 ± 0.21). The {alpha}2-adrenoceptor agonist clonidine was without any stimulatory effect on glucose uptake. The stimulatory effect of cirazoline was inhibited by the {alpha}1-adrenoceptor antagonist prazosin but not by the {beta}-adrenoceptor antagonist propranolol. RT-PCR showed that the {alpha}1A-adrenoceptor was the sole {alpha}1-adrenoceptor subtype expressed in L6 cells. Cirazoline or insulin-mediated glucose uptake was inhibited by the phosphatidylinositol-3 kinase inhibitor LY294002, suggesting a possible interaction between the {alpha}1-adrenoceptor and insulin pathways. Cirazoline or insulin stimulated phosphatidylinositol-3 kinase activity but {alpha}1-adrenoceptor activation did not phosphorylate Akt. Both cirazoline and insulin-mediated glucose uptake were inhibited by protein kinase C, phospholipase C and p38 kinase inhibitors, but not by Erk1/2 inhibitors (despite both treatments being able to phosphorylate Erk1/2). Insulin and cirazoline were able to activate and phosphorylate p38 kinase. The phorbol ester 12-O-tetradecanoylphorbol-13-acetate and the calcium ionophore A23187 produced significant increases in glucose uptake indicating a role for protein kinase C and calcium in glucose uptake. Down-regulation of conventional protein kinase C isoforms inhibited glucose uptake mediated by 12-O-tetradecanoylphorbol-13-acetate, but not by insulin or cirazoline. This study demonstrates that {alpha}1-adrenoceptors mediate increases in glucose uptake in L6 muscle cells. This effect appears to be related to activation of phospholipase C, phosphatidylinositol-3 kinase, p38 kinase and protein kinase C.
Key words: {alpha}1-Adrenoceptor • Glucose uptake • insulin • L6 cells




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