Is renin secreted by exocytotic mechanism through mature renin granules from juxtaglomerular cells?

Mature renin granules were isolated by the combination of discontinuous and continuous Percoll density gradient centrifugation. Stored renin in the renin granules was found to consist of isoelectrically seven different forms. The seven different isoelectric points (pIs) were 5.6, 5.35, 5.2, 5.0, 4.8, 4.6 and 4.4. Approximately 70% of the stored renin as the total enzymatic activities from all isoelectric peaks was found in a peak which pI corresponded to be 5.35. Renin secreted from isolated glomeruli was also focused into seven peaks possessing identical values. However, the distribution pattern of renin peaks was quite different from that of stored renin. In the secreted renin, peaks of 5.35 (pI) and 5.2 (pI) showed high renin activity and each had approximately 30% of released renin as the total recovered. These results indicate multiple forms of renin are stored and secreted by rat kidney. As the distribution pattern of enzymatic activities in renin peaks between stored renin and secreted renin are different, it is probable that renin may not secreted through mature renin granules by exocytotic mechanism.