Sulfonylureas are bound to a part of the b-cell cytoplasmic membrane potassium channel, called the sulfonylurea receptor (SUR, see Figure 27.1). This binding causes inhibition of the exit of potassium ions from the b-cell and a change of the cell's resting potential. This results in the opening of special calcium channels of the cytoplasmic
membrane, the entry of calcium ions inside the cell and the stimulation of insulin secretion. This is the way in which the response of the b-cell to glucose and other insulin-secreting stimuli (amino-acids, etc.) is ultimately performed. It is obvious that sulfonylureas act only when the capacity of the b-cell to produce insulin is intact.
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