alpha1A-adrenoceptors activate glucose uptake in L6 muscle cells through a phospholipase C-, phosphatidylinositol-3 kinase-, and atypical protein kinase C-dependent pathway.
The role of alpha1-adrenoceptor activation on glucose uptake in L6 cells was investigated. The alpha1-adrenoceptor agonist phenylephrine [pEC50 (-log10 EC50), 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 alpha2-adrenoceptor agonist clonidine was without any stimulatory effect on glucose uptake. The stimulatory effect of cirazoline was inhibited by the alpha1-adrenoceptor antagonist prazosin, but not by the beta-adrenoceptor antagonist propranolol. RT-PCR showed that the alpha1A-adrenoceptor was the sole alpha1-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 alpha1-adrenoceptor and insulin pathways. Cirazoline or insulin stimulated phosphatidylinositol-3 kinase activity, but alpha1-adrenoceptor activation did not phosphorylate Akt. Both cirazoline- and insulin-mediated glucose uptake were inhibited by protein kinase C (PKC), 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 roles for PKC and calcium in glucose uptake. Down-regulation of conventional PKC isoforms inhibited glucose uptake mediated by 12-O-tetradecanoylphorbol-13-acetate, but not by insulin or cirazoline. This study demonstrates that alpha1-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 PKC.
Hutchinson
Dana S
DS
Department of Physiology, The Wenner-Gren Institute, Arrhenius Laboratory F3, Stockholm University, SE 10691 Stockholm, Sweden.
Bengtsson
Tore
T
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D002273:Carcinogens / Q000494:pharmacology; D002460:Cell Line; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005947:Glucose / Q000493:pharmacokinetics*; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D010656:Phenylephrine / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D011224:Prazosin / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D018340:Receptors, Adrenergic, alpha-1 / Q000235:genetics / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D002273:Carcinogens; D048049:Extracellular Signal-Regulated MAP Kinases; D005947:Glucose; D007004:Hypoglycemic Agents; D007093:Imidazoles; D007328:Insulin; D007545:Isoproterenol; D010656:Phenylephrine; D019869:Phosphatidylinositol 3-Kinases; D011224:Prazosin; D011433:Propranolol; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger; D018340:Receptors, Adrenergic, alpha-1; D013755:Tetradecanoylphorbol Acetate; D010738:Type C Phospholipases; D048051:p38 Mitogen-Activated Protein Kinases; C547715:Adra1a protein, rat; C494920:Akt1 protein, rat; C115015:PKC-3 protein; C014282:cirazoline