Histochemical localization of carbonic anhydrase in the testis and epididymis of the rabbit.

The distribution of carbonic anhydrase (CA) was studied in the testis and epididymis of mature, male rabbits using a cobalt precipitation method. CA was found only in the endothelium of the capillaries in the testis. The epididymal duct was divided into initial, middle and terminal segments. Strong cytoplasmic CA was present in the apical cells in the initial and middle segments. Vacuoles with CA staining in the membranes were found in the principal cells in the middle segment. Intensely stained basal cells were present in the terminal segment. In the last part of the terminal segment and the first of the ductus deferens the basolateral cell membranes were also stained. The function of the enzyme is discussed especially in relation to acidification of the epididymal fluid and facilitation of CO2 diffusion.     

Depolarization and Neurotransmitters Increase Neuronal Protein Tyrosine Phosphorylation

Abstract: In rat hippocampal slices and in neurons in primary culture, K⁺-induced depolarization increased markedly and rapidly tyrosine phosphorylation of a 110-kDa protein (pp110) and, to a lesser degree, of a 120-kDa protein (pp120), in a calcium-dependent fashion. Qlutamate, 1-aminocyclopentane- trans -1,3-dicarboxylic acid (an agonist of metabotropic glutamate receptors), and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (an agonist of ionotropic glutamate receptors) stimulated also tyrosine phosphorylation of pp110 and pp120. These effects were not observed in astrocytes in primary culture. In hippocampal slices tyrosine phosphorylation of pp110 and pp120 was stimulated by Ca²⁺-ionophores and by phorbol esters and antagonized by a chelator of intracellular Ca²⁺and by drugs that inhibit protein kinase C. Stimulation of muscarinic and α₁,-adrenergic receptors increased also tyrosine phosphorylation of pp110 and pp120. These results demonstrate that membrane depolarization and stimulation of neurotransmitter receptors activate a tyrosine phosphorylation pathway in neurons. This pathway involves an increase in intracellular Ca²⁺ concentrations and the activation of protein kinase C. It may provide a biochemical basis for some neurotrophic effects of electrical activity and neurotransmitters and may contribute to the role of tyrosine phosphorylation in long-term potentiation.