Suppression of potassium conductance by droperidol has influence on excitability of spinal sensory neurons

Background: During spinal and epidural anesthesia with opioids, droperidol is added to prevent nausea and vomiting. The mechanisms of its action on sp inal sensory neurons are not well understood. It was previously shown that droperidol selectively blocks a fast component of the Na+ current. The auth ors studied the action of droperidol on voltage-gated K+ channels and its e ffect on membrane excitability in spinal dorsal horn neurons of the rat. Methods: Using a combination of the patch-clamp technique and the "entire s oma isolation" method, the action of droperidol on fast-inactivating A-type and delayed-rectifier K+ channels was investigated. Current-clamp recordin gs from intact sensory neurons in spinal cord slices were performed to stud y the functional meaning of K+ channel block for neuronal excitability, Results: Droperidol blocked delayed-rectifier K+ currents in isolated somat a of dorsal horn neurons with a half-maximum inhibiting concentration of 20 .6 muM. The A-type K+ current was insensitive to up to 100 muM droperidol, At droperidol concentrations insufficient for suppression of an action pote ntial, the block of delayed-rectifier K+ channels led to an increase in act ion potential duration and, as a consequence, to lowering of the discharge frequency in the neuron. Conclusions: Droperidol blocks delayed-rectifier K+ channels in a concentra tion range close to that for suppression of Na+ channels. The block of dela yed-rectifier K+ channels by droperidol enhances the suppression of activit y in spinal sensory neurons at drug concentrations insufficient for complet e conduction block.