Quinine blocks the high conductance, calcium‐activated potassium channel in rat pancreatic β‐cells

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Abstract
The [Ca2+]i-activated K+-channel, one of the 3 K+-channels described in pancreatic β-cells, is a high conductance, voltage-dependent K+-channel. Quinine, known to block [Ca2+]i-activated K+-channels in other cells, has been described to block the silent phase between the bursts of glucose-evoked electrical activity in mouse pancreatic β-cells, and to inhibit K+ efflux from rat pancreatic islets. We report here that quinine blocks the [Ca2+ i-activated K+-channel in rat pancreatic β-cells, from the external side of the membrane. We also show that the blockade is characterized by fast flickering of the K+-channel between the open and closed state. Mean open and closed times within bursts were found to be exponentially distributed, suggesting that the blockade by quinine involves obstruction on the K+ flow through the open to be exponentially distributed, suggesting that the blockade by quinine involves obstruction on the K+ flow through the open channel.