Cytochrome reduction induced by increase in extracellular potassium and by electrical stimulation in isolated perifused neurohypophysis of guinea pig under mild hypoxic conditions.

Parallel reduction of cytochromes, a(a3), b and c + c1 was recorded under mild hypoxic conditions when the neurohypophysis was electrically stimulated and extracellular KCl concentration was increased. The electrically stimulated reduction was abolished by tetrodotoxin and by replacement of NaCl with LiCl. The reduction was not influenced by removal of extracellular Ca2+, or by application of a Ca ionophore, A23187. These results show that cytochrome reduction correlates with K+-influx in the resting state, and with Na+-influx followed by activation of the neurosecretory terminals contained in the neurohypophysis.