Previous studies has report the modulation of K channels play key roles in the induction of peripheral antinociception induced by many types of drugs. However. the possible participation of 4-aminopyridine-sensitive K+ channels to local antinociception induced by tramadol, a mu opioid receptor agonist, and lidocaine, a local anaesthetic, has been less studied. In this study, we therefore investigated this by using thermal plantar test. Tramadol or lidocaine administered intraplantarly into the hind paw elicited an antinociceptive effect. 4-aminopyridine caused an increase in the antinociception produced by lidocaine. However, tramadol induced antinociception remained unaffected by intraplantar administration of 4-aminopyridine. These results suggest that 4-aminopyridine-sensitive K+ channels may play an important role in the thermal peripheral antinociception produced by lidocaine, but not tramadol. (c) 2007 Elsevier B.V. All rights reserved.