Activating effect of the flavonoid phloretin on Ca(2+)-activated K+ channels in myelinated nerve fibers of Xenopus laevis [corrected].
The effects of the flavonoid phloretin on K+ channels in amphibian myelinated nerve were studied by patch clamping. The open probability of Ca(2+)-activated K+ channels was greatly increased by external phloretin (10-200 microM) due to a shift of the membrane potential for half-maximal activation, E50, of -63.9 mV (80 microM phloretin). Open times were prolonged and closed times shortened. Channel activation by phloretin developed slowly (tau on = 33.4 s) and its washout was even slower (tau off,1 = 4.7 and tau off,2 = 183.2 s). In contrast, submillimolar phloretin blocked two delayed rectifier K+ channels (I and F) whereas the gating of the ATP-sensitive and the flickering K+ channel were unaffected. Phloretin may directly affect the voltage sensor of K+ channels.
Physiologisches Institut, Justus-Liebig-Universität, Giessen, Germany.
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Koh
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Reid
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Vogel
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001369:Axons / Q000378:metabolism / Q000502:physiology; D002118:Calcium / Q000502:physiology*; D004594:Electrophysiology; D015640:Ion Channel Gating / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D009413:Nerve Fibers, Myelinated / Q000187:drug effects / Q000378:metabolism*; D010693:Phloretin / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects*; D014982:Xenopus laevis
D015221:Potassium Channels; D000255:Adenosine Triphosphate; D010693:Phloretin; D002118:Calcium