Inhibition of the ATP-sensitive potassium channel from mouse pancreatic beta-cells by surfactants.
1. We have used patch-clamp methods to study the effects of the detergents, Cremophor, Tween 80 and Triton X100 on the K(ATP) channel in the pancreatic beta-cell from mouse. 2. All three detergents blocked K(ATP) channel activity with the following order of potency: Tween 80 (Ki< approximately 83 nM)>Triton X100 (Ki=350 nM)>Cremophor. In all cases the block was poorly reversible. 3. Single-channel studies suggested that at low doses, the detergents act as slow blockers of the K(ATP) channel. 4. Unlike the block produced by tolbutamide, that produced by detergent was not affected by intracellular Mg2+-nucleotide, diazoxide or trypsin treatment, nor did it involve an acceleration of rundown or increase in ATP sensitivity of the chanel. 5. The detergents could block the pore-forming subunit, Kir6.2deltaC26, which can be expressed independently of SUR1 (the regulatory subunit of the K(ATP) channel). These data suggest that the detergents act on Kir6.2 and not SUR1. 6. The detergents had no effect on another member of the inward rectifier family: Kir1.1a (ROMK1). 7. Voltage-dependent K-currents in the beta-cell were reversibly blocked by the detergents with a far lower potency than that found for the K(ATP) channel. 8. Like other insulin secretagogues that act by blocking the K(ATP) channel, Cremophor elevated intracellular Ca2+ in single beta-cells to levels that would be expected to elicit insulin secretion. 9. Given the role of the K(ATP) channel in many physiological processes, we conclude that plasma borne detergent may have pharmacological actions mediated through blockage of the K(ATP) channel.
Smith
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University Laboratory of Physiology Parks Road, Oxford, UK.
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D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D004558:Electric Stimulation; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects*; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D013501:Surface-Active Agents / Q000494:pharmacology*; D014981:Xenopus
D007328:Insulin; D026902:Potassium Channel Blockers; D013501:Surface-Active Agents; D000255:Adenosine Triphosphate; D002118:Calcium