Effect of ouabain and potassium-free solution on mammalian thermosensitive afferents in vitro

Studies have been performed on the afferent fibers innervating the scrotal skin of the rat to test the hypothesis that the generator potential mechanism underlying cold thermosensitivity of these afferent fibers is an electrogenic sodium pump. In these experiments a pudendal nerve-scrotal skin preparation was isolated from the animal and maintained in oxygenated mammalian Ringer's where composition could be varied and drugs added. Application of ouabain resulted in an increae in the discharge of cold sensitive afferent fibers which was more pronounced at 38--41 degrees C than at temperature below 30 degrees C. In most of the cases transient accelerations on cooling were reduced, but often a transient response to warming appeared. The effects of ouabain administration were reversible. Removal of extracellular K at 35 degrees C resulted in an increased discharge of cold sensitive afferents. This observation is consistent with the effects of ouabain, since removal of extracellular K also block Na transport. The generator potential mechanism underlying cold sensitivity of these afferent fibers appears to be an electrogenic Na pump.