... that is in turn thought to promote insulin secretion by depolarising the cell, that is, by making the resting potential become more positive. IF 15mM of glucose is added to a beta-cell within an isolated Islet of Langerhans, within about a minute its membrane potential is found to change from its resting potential of about -60mV to -30mV. This depolarization is a consequence of the decrease in the membrane's permeability to potassium ions that is observed in the presence of glucose. It has recently been possible to obtain records of a single ion channel in a patch of membrane on an intact beta-cell, thanks to a technique known as "cell-attached patch-clamp recording". These records show the current level when the ion channel is in the open and closed state, allowing one to calculate the proportion of time that the channel is open, or the "open-state probability". In the complete absence ...

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