The action of capsaicin on type I delayed rectifier K + currents in rabbit Schwann cells

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Abstract
Capsaicin, a lipophilic alkaloid, blocked type I K$^{+}$ currents in rabbit cultured Schwann cells when applied by superfusion. The concentration--response relation at equilibrium was well described by a rectangular hyperbola, with a K$_{\text{D}}$ of 8.7 $\mu $M. The kinetics of block resembled an `inactivation', the rate of blockade increasing with increasing concentrations of capsaicin (1-100 $\mu $M). Unlike internal tetraethylammonium (TEA) ions (5-10 mM), which preferentially reduced outward current in symmetrical high [K$^{+}$], capsaicin reduced both inward and outward type I current by the same proportion. The block achieved by capsaicin during a voltage-clamp step that activated the current was relieved by subsequent hyperpolarization, and the rate of relief from block at -70 mV and -100 mV could be reasonably accounted for on the assumption that capsaicin had to unbind to allow the channels to close.