Large dense-core vesicles in rat adrenal after reserpine: levels of mRNAs of soluble and membrane-bound constituents in chromaffin and ganglion cells indicate a biosynthesis of vesicles with higher secretory quanta.

Abstract

Rats were injected with a large dose of reserpine known to stimulate the adrenal medulla. Various times after drug treatment the mRNA levels of several constituents of large dense-core vesicles were determined by northern blot analysis and in situ hybridization. The latter method allowed detection of changes in mRNA levels not only in chromaffin cells, but also in the ganglion cells found in adrenal medulla. Levels of the mRNAs of secretory components of large dense-core vesicles (chromogranins A and B, secretogranin II, VGF, and neuropeptide Y) increased in chromaffin cells by 215-857% after 1-3 days of drug treatment. For partly membrane-bound components (dopamine beta-hydroxylase, prohormone convertase 2, carboxypeptidase H, and peptidylglycine alpha-amidating monooxygenase) the changes ranged from 182 to 315%, whereas for glycoprotein III and for intrinsic membrane proteins (cytochrome b561 and vesicle monoamine transporter 2) no change occurred. In ganglion cells the mRNAs that could be detected for VGF, neuropeptide Y, secretogranin II, carboxypeptidase H, and vesicle monoamine transporter 1 showed an analogous pattern of change, with significant increases for the secretory proteins and no change for the membrane components. From these and previous results we suggest the following concept: Long-lasting stimulation of chromaffin cells or neurons does not induce the biosynthesis of a larger number of vesicles but rather leads to the formation of vesicles containing higher secretory quanta of chromogranins and neuropeptides.