Mechanical Hyperalgesia Induced by Blocking Calcium-activated Potassium Channels on Capsaicin-sensitive Afferent Fiber

Mechanical Hyperalgesia Induced by Blocking Calcium-activated Potassium Channels on Capsaicin-sensitive Afferent Fiber

Small and large conductance Ca<SUP>2+</SUP>-activated K<SUP>+</SUP> (SK<SUB>Ca</SUB> and BK<SUB>Ca</SUB>) channels are implicated in the modulation of neuronal excitability. We investigated how changes in peripheral K<SUB>Ca</SUB> channel activity affect mechanical sensitivity as well as the afferent fiber type responsible for K<SUB>Ca</SUB> channel-induced mechanical sensitivity. Blockade of SK<SUB>Ca</SUB> and BK<SUB>Ca</SUB> channels induced a sustained decrease of mechanical threshold which was significantly attenuated by topical application of capsaicin onto afferent fiber and intraplantar injection of 1-ethyl-2-benzimidazolinone. NS1619 selectively attenuated the decrease of mechanical threshold induced by charybdotoxin, but not by apamin. Spontaneous flinching and paw thickness were not significantly different after K<SUB>Ca</SUB> channel blockade. These results suggest that mechanical sensitivity can be modulated by K<SUB>Ca</SUB> channels on capsaicin-sensitive afferent fibers.