Ultracytochemical localization of ouabain-sensitive, potassium-dependent p-nitrophenylphosphatase activity in guinea pig retina. II. Neurons and Mueller cells.

Abstract

Ouabain-sensitive, K-dependent p-nitrophenylphosphatase (K-NPPase) activity, which reflects the second dephosphorylative step of Na-K-ATPase, was investigated histochemically under light and electron microscopes in neurons and Müller cells of the normal adult guinea pig retina with the newly eveloped one step lead citrate method (Mayahara et at., 1980). In guinea pig retina fixed for 5min in a mixture of 2% paraformaldehyde and 0.25% glutaraldehyde, electron dense reaction precipitates indicating K-NPPase activity were observed on plasma membranes of neurons and Müller cells. The most intensive K-NPPase reaction products were evident in the post-synaptic membranes of neurons in the outer plexiform layer, presynaptic membranes of neurons and post-synaptic membranes of ganglion cells and in the processes of Müller cells in the inner plexiform layer. This reaction was almost completely abolished by 10mM ouabain or elimination of K. The activity was also substrate-dependent, and completely inhibited by PCMB-S or preheating.It is noteworthy that another p-nitrophenylphosphatase activity which is ouabain-insensitive, Levamisole-resistant and K-independent was recognized on the endoplasmic reticulum, Golgi apparatus and nuclear envelope solely in Müller cells. This activity was also substrate-dependent, and completely inhibited by PCMB-S or preheating.Mg-ATPase activity was observed only on the synaptic membranes of neurons and ganglion cells in the inner plexiform layer. However, this reaction could be neither inhibited by ouabain nor activated by K. Non-specific alkaline phosphatase activity was not demonstrated on any part of the plasma membranes of neurons, ganglion cells or Müller cells.