Expression and function of Connexin 43 and Connexin 37 in the murine zona glomerulosa.

The zona glomerulosa (ZG) synthesizes the mineralocorticoid aldosterone. The primary role of aldosterone is the maintenance of volume and electrolyte homeostasis. Aldosterone synthesis is primarily regulated via tightly controlled oscillations in intracellular calcium levels in response to stimulation. It has previously been shown that calcium oscillations are synchronized through mechanical linkage between adjacent ZG cells. In many other cell types, similar synchronization is rather dependent on gap junctions (GJ). The recent discovery of mutations in CADM1 was linked to impaired GJ function in the ZG. Based on published transcriptomics data, we re-examined the presence and functional impact of GJ in the ZG. We found evidence for the expression of murine connexin 43 and 37 using microarray data, in-situ hybridization and immunohistology. Connexin 43 was also present in human samples. Calcium oscillations in ZG rosettes showed some degree of synchronization as reported previously. Unspecific GJ inhibition only had a small impact on this synchronicity. However, no signs of connections between cytosols could be observed as indicated by the lack of fluorescence recovery after photobleaching. We conclude that, while connexin proteins are expressed in the ZG, functional GJ in the physiological ZG are rare and of little consequence for calcium signaling.