Dual actions of the metabolic inhibitor, sodium azide on K ATP channel currents in the rat CRI‐G1 insulinoma cell line

The effects of various inhibitors of the mitochondrial electron transport chain on the activity of ATP‐sensitive K + channels were examined in the Cambridge rat insulinoma G1 (CRI‐G1) cell line using a combination of whole cell and single channel recording techniques. Whole cell current clamp recordings, with 5 m M ATP in the pipette, demonstrate that the mitochondrial uncoupler sodium azide (3 m M ) rapidly hyperpolarizes CRI‐G1 cells with a concomitant increase in K + conductance. This is due to activation of K ATP channels as the sulphonylurea tolbutamide (100 μ M ) completely reversed the actions of azide. Other inhibitors of the mitochondrial electron transport chain, rotenone (10 μ M ) or oligomycin (2 μ M ) did not hyperpolarize CRI‐G1 cells or increase K + conductance. In cell‐attached recordings, bath application of 3 m M sodium azide (in the absence of glucose) resulted in a rapid increase in K ATP channel activity, an action readily reversible by tolbutamide (100 μ M ). Application of sodium azide (3 m M ), in the presence of Mg‐ATP, to the intracellular surface of excised inside‐out patches also increased K ATP channel activity, in a reversible manner. In contrast, rotenone (10 μ M ) or oligomycin (2 μ M ) did not increase K ATP channel activity in either cell‐attached, in the absence of glucose, or inside‐out membrane patch recordings. Addition of sodium azide (3 m M ) to the intracellular surface of inside‐out membrane patches in the presence of Mg‐free ATP or the non‐hydrolysable analogue 5′‐adenylylimidodiphosphate (AMP‐PNP) inhibited, rather than increased, K ATP channel activity. In conclusion, sodium azide, but not rotenone or oligomycin, directly activates K ATP channels in CRI‐G1 insulin secreting cells. This action of azide is similar to that reported previously for diazoxide. British Journal of Pharmacology (1999) 126 , 51–60; doi: 10.1038/sj.bjp.0702267