glucagon secretion from the a cell has been closely examined , even the supposition that low glucose stimulates a cells to secrete glucagon while high glucose causes cessation of glucagon release remains in debate. The mechanism by which high glucose suppresses a cell secretion has been attributed not only to somatostatin but also to additional inhibitory paracrine factors secreted by the adjacent b cells (insulin, Zn2+, GABA) in responseto high glucose . These paracrine factors inhibit a cell glucagon secretion by variously causing membrane hyperpolarization to dampen a cell excitability. Somatostatin hyperpolarizes a cells by activating a low-conductance K+ channel coupled to inhibitory G proteins, while GABA hyperpolarizes a cells by activating Cl! influx