ELECTRON-MICROSCOPIC IMMUNOLOCALIZATION OF CALTRIN PROTEINS IN GUINEA-PIG SEMINAL-VESICLES

Caltrins, the small, basic proteins of the seminal vesicle secretion t hat inhibit calcium transport into epididymal spermatozoa, and consequ ently the onset of the acrosome reaction and the hyperactivated motili ty, were localized in the epithelial cells and the lumen of the semina l vesicles of the guinea pig by an immunocytochemical procedure and el ectron microscopy. Rabbit antisera against each protein (caltrin I or II), and goat anti-rabbit IgG antiserum labeled with colloidal gold we re used to detect the caltrin immunoreaction. The subcellular distribu tion of the gold labeling was occasionally localized in the rough endo plasmic reticulum but mainly within big secretory vacuoles containing low electron-dense material, which are components of the Golgi complex known as condensing vacuoles. These are involved in the intracellular transport, storage, and discharge of secretory proteins. Gold-labeled material released to the lumen was also detected. There was no clear evidence that the discharge was mediated by an exocytotic process. Imm unoreaction was observed neither in the electron-dense core nor in the electron-lucent halo of the typical secretory granules of the epithel ial cells of the seminal vesicles. Using light microscope immunocytoch emistry, intense positive immunoreactivity was detected in the materia l secreted to the lumen but not on the epithelial cell laser. Only tho se cells undergoing a degenerative process and showing a picnotic nucl eus and condensed cytoplasmic matrix exhibited detectable immunoreacti on when gold label and silver intensification were applied. The same d istribution of the immunoprobes was obtained by electron or light micr oscopy when antiserum to either I or II was used. It would appear that the two caltrin proteins of the guinea pig are synthesized in the rou gh endoplasmic reticulum of the epithelial cells and transported quick ly to the Golgi complex where the secretory vacuoles (condensing vacuo les) are formed. The proteins are transported by the secretory vacuole s to the apical ends of the cells to be discharged into the lumen.