Characterization of the beta-adrenoceptor subtype involved in mediation of glucose transport in L6 cells.
1. The receptor that mediates the increase in glucose transport (GT) in response to beta-adrenoceptor (beta-AR) agonists was characterized in the rat skeletal muscle cell line L6, using the 2-deoxy-[(3)H]-D-glucose assay. 2. The beta(3)-AR agonist BRL37344 (pEC(50) = 6.89 +/- 0.21), the beta-AR agonist isoprenaline (pEC(50) = 8.99 +/ -0.24) and the beta(2)-AR agonist zinterol (pEC(50) = 9.74 +/- 0.15) increased GT as did insulin (pEC(50) = 6.93 +/- 0.15). The highly selective beta(3)-AR agonist CL316243 only weakly stimulated GT. 3. The pK(B) values calculated from the shift of the pEC(50) values of the agonists in the presence of the beta(1)-AR selective antagonist CGP 20712A or the beta(3)-AR selective antagonist SR 59230A were not indicative of activation of beta(1)- or beta(3)-ARs. Only (-)-propranolol and the beta(2)-AR selective antagonist ICI 118551 caused marked rightward shifts of CR curves to isoprenaline (pK(B) = 10.2 +/- 0.2 and 9.6 +/- 0.3), zinterol (pK(B) = 9.0 +/- 0.1 and 9.4 +/- 0.3) and BRL 37344 (pK(B) = 9.4 +/- 0.3 and 8.4 +/- .2), indicating participation of beta(2)-ARs. 4. The pharmacological analysis was supported by reverse transcription and polymerase chain reaction analysis of L6 mRNA, which showed high levels of expression of beta(2)-AR but not beta(1)- or beta(3)-AR in these cells. 5. Forskolin and dibutyryl cyclic AMP produced negligible increases in GT while the phosphatidylinositol-3 kinase inhibitor, wortmannin, significantly decreased both insulin- and zinterol-stimulated GT, suggesting a possible interaction between the insulin and beta(2)-AR pathways. 6. This study demonstrates that beta(2)-ARs mediate the increase in GT in L6 cells to beta-AR agonists, including the beta(3)-AR selective agonist BRL 37344. This effect does not appear to be directly related to increases in cyclic AMP but requires P13K.
Nevzorova
Julia
J
Department of Pharmacology, PO Box 13E, Monash University, Victoria 3800, Australia.
Bengtsson
Tore
T
Evans
Bronwyn A
BA
Summers
Roger J
RJ
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D003994:Bucladesine / Q000494:pharmacology; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology / Q000502:physiology; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000077191:Wortmannin
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D000730:Androstadienes; D007328:Insulin; D012333:RNA, Messenger; D011943:Receptors, Adrenergic, beta; D005576:Colforsin; D003994:Bucladesine; D005947:Glucose; D000077191:Wortmannin