IMMUNOLOGICAL LOCALIZATION AND KINETIC CHARACTERIZATION OF A NA+ CA2+EXCHANGER IN NEURONAL AND NONNEURONAL CELLS/

The plasma membrane Na+/Ca2+ exchanger is believed to play a role in t he regulation of Ca2+ fluxes in neurons, though the lack of specific i nhibitors has limited the delineation of its precise contribution. We recently reported the development of antibodies against a 36-kDa brain synaptic membrane protein which immunoprecipitated exchanger activity from solubilized membranes. In the present study we examined the kine tics of the Na+/Ca2+ exchanger in primary neurons in culture, in a neu ronal hybrid cell line (NCB-20), and in a fibroblast-like cell line (C V-1) to see whether the level of exchanger activity correlated with th e degree of immunostaining produced by our antibodies. The V-max was d etermined for each cell type and found to be highest in primary neuron s. Exchanger activity increased in primary neurons between days 1 and 6 in culture, but no such time-dependent change occurred in either of the cell lines. Immunoblot analysis of the three cell types probed wit h the anti-36-kDa protein antibodies revealed significantly greater im munostaining in the primary neurons compared with the other two cell t ypes. Intensity of staining of neurons also increased significantly be tween days 1 and 6 in culture. Immunocytochemistry showed significant labelling of the primary neurons on the neuritic processes and points of contact between cells. The NCB-20 and CV-1 cells showed considerabl y lower levels of immunoreactivity. The antibodies immunoextracted sim ilar to 90% of the exchanger activity in the primary neurons and simil ar to 70 and 50% of the activity in NCB-20 and CV-1 cells respectively . Thus the expression of the 36-kDa protein appears to be closely asso ciated with the Na+/Ca2+ exchanger in neuronal cells and, possibly to a lesser extent, in non-neuronal cells.