DIFFERENCES IN THE DISTRIBUTION OF PROTEINS ASSOCIATED WITH OMEGA-CONOTOXIN RECEPTORS IN RAT PITUITARY-CELLS

Two monoclonal antibodies, SPM-1 and SPM-2, raised against brain synap tic membrane specifically recognized two different omega-conotoxin rec eptor-associated proteins with molecular masses of 36 kDa and 28 kDa, respectively. In the anterior lobe of the rat pituitary, all secretory cells were immunostained with SPM-2, but not with SPM-1, although fol liculo-stellate cells were stained with both SPM-1 and SPM-2. Castrati on or stimulation with hypothalamic hormones caused an increase in the intensity of the SPM-2 staining in hormone-secretory cells. In the in termediate lobe, all secretory cells showed a strong 28-kDa-protein im munoreactivity. In the posterior lobe, the immunoreactivity to both SP M-1 and SPM-2 was recognized in nerve endings. The results demonstrate that hormone-secretory cells in the anterior and intermediate pituita ry possess only 28-kDa protein, and thus two omega-conotoxin receptor- associated proteins (36 kDa and 28 kDa) are not necessarily colocalize d in these cells.