Abstract
The mechanisms by which insulin modulates neuronal plasticity and pain processes remain poorly understood. Here we report that insulin rapidly increases the function of glycine receptors in murine spinal neurons and recombinant human glycine receptors expressed in human embryonic kidney cells. Whole-cell patch-clamp recordings showed that insulin reversibly enhanced current evoked by exogenous glycine and increased the amplitude of spontaneous glycinergic miniature inhibitory postsynaptic currents recorded in cultured spinal neurons. Insulin (1 μM) also shifted the glycine concentration-response plot to the left and reduced the glycine EC50 value from 52 to 31 μM. Currents evoked by a submaximal concentration of glycine were increased to approximately 140% of control. The glycine receptor α subunit was sufficient for the enhancement by insulin because currents from recombinant homomeric α1 receptors and heteromeric α1β receptors were both increased. Insulin acted at the insulin receptor via pathways dependent on tyrosine kinase and phosphatidylinositol 3 kinase because the insulin effect was eliminated by the insulin receptor antagonist, hydroxy-2-naphthalenylmethylphosphonic acid trisacetoxymethyl ester, the tyrosine kinase inhibitor lavendustin A, and the phosphatidylinositol 3 kinase antagonist wortmannin. Together, these results show that insulin has a novel regulatory action on the potency of glycine for ionotropic glycine receptors.
Footnotes
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This research is supported by operating grants from the Canadian Institutes of Health Research (to B.A.O.) (MOP-38028), a Career Scientist Award (to B.A.O.), a Canadian Institutes of Health Research doctoral research award (to V.B.C.) (56381) and postdoctoral fellowship award (to J.G.N.) (63508). B.A.O. is a Canada Research Chair in Anesthesia.
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B.A.O. serves as a scientific advisor to Merck Sharp and Dohme Inc.
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Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
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doi:10.1124/mol.106.033563.
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ABBREVIATIONS: GlyR, glycine receptor; GABAA, γ-aminobutyric acid subtype A; PKC, protein kinase C; PI3, phosphatidylinositol 3; MEM, minimum essential medium; FBS, fetal bovine serum; DIV, days in vitro; HEK, human embryonic kidney; mIPSC, miniature inhibitory postsynaptic current; HNMPA, hydroxyl-2-naphthalenylmethylphosphonic acid trisacetoxymethyl ester; DMSO, dimethyl sulfoxide; PBS, phosphate-buffered saline; IGly, glycine current; NMDA, N-methyl-d-aspartate; IGF, insulin-like growth factor.
- Received December 22, 2006.
- Accepted February 15, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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