Premium
Multiple signalling pathways involved in β 2 ‐adrenoceptor‐mediated glucose uptake in rat skeletal muscle cells
Author(s) -
Nevzorova Julia,
Evans Bronwyn A,
Bengtsson Tore,
Summers Roger J
Publication year - 2006
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0706626
Subject(s) - forskolin , endocrinology , medicine , biology , protein kinase a , cholera toxin , stimulation , kinase , microbiology and biotechnology
β ‐adrenoceptor (AR) agonists increase 2‐deoxy‐[ 3 H]‐ D ‐glucose uptake (GU) via β 2 ‐AR in rat L6 cells. The β ‐AR agonists, zinterol ( β 2 ‐AR) and (−)‐isoprenaline, increased cAMP accumulation in a concentration‐dependent manner (pEC 50 =9.1±0.02 and 7.8±0.02). Cholera toxin (% max increase 141.8±2.5) and the cAMP analogues, 8‐bromo‐cAMP (8Br‐cAMP) and dibutyryl cAMP (dbcAMP), also increased GU (196.8±13.5 and 196.4±17.3%). The adenylate cyclase inhibitor, 2′,5′‐dideoxyadenosine (50 μ M ), significantly reduced cAMP accumulation to zinterol (100 n M ) (109.7+35.0 to 21.6+4.5 pmol well −1 ), or forskolin (10 μ M ) (230.1±58.0 to 107.2±26.3 pmol well −1 ), and partially inhibited zinterol‐stimulated GU (217±26.3 to 176.1±20.4%). The protein kinase A (PKA) inhibitor, 4‐cyano‐3‐methylisoquinoline (100 n M ), did not inhibit zinterol‐stimulated GU. The PDE4 inhibitor, rolipram (10 μ M ), increased cAMP accumulation to zinterol or forskolin, and sensitised the GU response to zinterol, indicating a stimulatory role of cAMP in GU. cAMP accumulation studies indicated that the β 2 ‐AR was desensitised by prolonged stimulation with zinterol, but not forskolin, whereas GU responses to zinterol increased with time, suggesting that receptor desensitisation may be involved in GU. Receptor desensitisation was not reversed by inhibition of PKA or Gi. PTX pretreatment (100 ng ml −1 ) inhibited insulin or zinterol‐stimulated but not 8Br‐cAMP or dbcAMP‐stimulated GU. The PI3K inhibitor, LY294002 (1 μ M ), inhibited insulin‐ (174.9±5.9 to 142.7±2.7%) and zinterol‐ (166.9±7.6 to 141.1±8.1%) but not 8 Br‐cAMP‐stimulated GU. In contrast to insulin, zinterol did not cause phosphorylation of Akt. The results suggest that GU in L6 cells involves three mechanisms: (1) an insulin‐dependent pathway involving PI3K, (2) a β 2 ‐AR‐mediated pathway involving both cAMP and PI3K, and (3) a receptor‐independent pathway suggested by cAMP analogues that increase GU independently of PI3K. PKA appears to negatively regulate β 2 ‐AR‐mediated GU.British Journal of Pharmacology (2006) 147 , 446–454. doi: 10.1038/sj.bjp.0706626