Episodic release of renin from single isolated superfused rat afferent arterioles

Doubts have been raised about the involvement of an exocytotic event in the renin release process. This motivated the development of a technique which permitted the study of renin release from one single superfused rat afferent arteriole with a time resolution of 20 seconds. By using this technique it is shown in 43 experiments that the undisturbed renin release is episodic with a renin discharge of 45.2 +/- 3.3 (SEM) nano Goldblatt units per episode (n = 114) and a frequency of one episode per 5 min. The total renin content of one arteriole was about 30 microGU. The renin discharge and frequency correspond to calculated values for the renin content of single juxtaglomerular cell granules and the release rates in vivo, respectively. Release activity could be stimulated by an acute decrease in the osmolality of the superfusion medium (-20 mOsm sucrose, n = 14) indicating that an osmotic water movement is involved in the secretory process. This study provides functional evidence that renin release is exocytotic. In addition it reports what appears to be the first direct measurement of release of secretory material compatible with secretion of single granules from any secretory system.