Activation of muscarinic M1 receptors by acetylcholine to increase glucose uptake into cultured C2C12 cells.

Regulation of glucose metabolism by cholinergic nervous activation has been demonstrated. In an attempt to evaluate the role of cholinergic receptor subtype in this regulation of glucose metabolism, we employed cultured myoblast C2C12 cells to investigate the glucose uptake in the present study. Acetylcholine (ACh) enhanced the uptake of radioactive glucose into C2C12 cells at the concentration range of 0.001 to 1.0 micromol/l. This effect was suppressed by the muscarinic antagonist atropine. Effect of ACh on muscarinic receptors was further supported by the blockade of scopolamine, another classical antagonist. Thus, activation of muscarinic receptors to enhance the radioactive glucose uptake into C2C12 cells can be considered. Moreover, pirenzepine, the antagonist of muscarinic M1 receptors, competitively antagonized the action of ACh in C2C12 cells. However, methoctramine at concentration sufficient to inhibit the muscarinic M2 receptors failed to produce similar effect. Similarly, 4-DAMP at effective concentration to block muscarinic M3 receptors lacked the influence. An activation of muscarinic M1 receptors seems responsible for the action of ACh in C2C12 cells. Pharmacological inhibition of phospholipase C by U73312 resulted in a concentration-dependent decrease in ACh-stimulated uptake of radioactive glucose into C2C12 cells. However, treatment with U73343, the inactive congener, failed to block the action of ACh. Moreover, both chelerythrine and GF 109203X diminished the action of ACh at concentrations sufficient to inhibit protein kinase C. Therefore, the obtained data suggest that increase of the glucose uptake evoked by ACh is mainly due to the activation of muscarinic M1 receptors in cultured myoblast C2C12 cells.