Angiotensin II elicits robust calcium oscillations coordinated within juxtaglomerular cell clusters to suppress renin secretion

Background: Juxtaglomerular (JG) cells are sensors that control blood pressure and fluid-electrolyte homeostasis. In response to a decrease in perfusion pressure or changes in the composition and/or volume of the extracellular fluid, JG cells release renin, which initiates an enzymatic cascade that culminates in the production of angiotensin II (Ang II), a potent vasoconstrictor that restores blood pressure and fluid homeostasis. In turn, Ang II exerts a negative feedback on renin release, thus preventing excess circulating renin and the development of hypertension. How Ang II suppresses renin release from JG cells remains elusive. Ang II may inhibit renin release via increased systemic pressure sensed by JG cells, or through a direct effect on Ang II receptors in JG cells, which in turn mediate intracellular calcium (Ca²⁺) mobilization, a known suppressor of renin release. However, the intricate cellular events mediating Ca²⁺-induced renin inhibition by Ang II are not fully understood. Further, the unique structural organization of the juxtaglomerular apparatus (JGA), with JG cells clustered around afferent arterioles, suggests complex intercellular interactions, potentially facilitating coordinated Ca²⁺ activity in response to Ang II. Here, we investigate the cellular processes that control Ca²⁺ mobilization and the signaling mechanisms elicited when JG cells are stimulated with Ang II within the intact anatomical context of the JGA. By examining these processes, we aim to elucidate the role of cellular organization in Ca²⁺-mediated signaling and its impact on renin regulation within the JGA.

Objective: To define intra- and inter-cellular Ca²⁺ dynamics, identify the driving ion channels, and elucidate their functional role in Ang II-stimulated JG cells within the native kidney structure.

Methods and results: We generated mice expressing JG cell-specific GCaMP6f, a genetically encoded Ca²⁺ indicator, under the Ren1 ^c promoter. Ex vivo Ca²⁺ imaging in acutely prepared kidney slices revealed that JG cells within clusters exhibit coordinated, robust Ca²⁺ oscillations in response to Ang II stimulation, contrary to previous observations in isolated cells. These oscillations showed dose-dependent increases in occurrence and correlated with suppressed renin secretion. Pharmacological inhibition identified key drivers of these oscillations: endoplasmic reticulum Ca²⁺ storage and release, extracellular Ca²⁺ uptake via ORAI channels, and intercellular communication through gap junctions. Blocking ORAI channels and gap junctions alleviated Ang II inhibition of renin secretion.

Conclusion: In intact kidney slices, Ang II elicits synchronized Ca²⁺ oscillations in JG cells, driven by endoplasmic reticulum-derived Ca²⁺ release, ORAI channels, and gap junctions, leading to suppressed renin secretion.