Block by the neuropeptide TRH of an apparently novel K+ conductance of rat motoneurones.

Using a single electrode voltage clamp technique the actions of rapidly superfused thyrotropin-releasing hormone (TRH, 1 microM) on lumbar motoneurones of the isolated neonatal rat spinal cord were investigated. TRH induced a slowly developing inward current (associated with an input conductance fall) with slow recovery on washout. In the presence of TRH the normally linear current-voltage relations displayed strong inward rectification up to about -40 mV. The TRH-induced current peaked at -50 mV, reversed at -120 mV and was not blocked by Cs+, tetraethylammonium, 4-aminopyridine, Cd2+, or low Na+. Its reversal potential was sensitive to changes in extracellular K+. Ba2+ (0.2-1.5 mM) depressed the effects of TRH. It is suggested that in rat motoneurones TRH blocked an apparently novel K+ conductance (IK(T)) active at resting membrane potential.