Abstract Body: Introduction: Juxtaglomerular (JG) cells play a crucial role in regulating blood pressure and fluid-electrolyte homeostasis by secreting renin in response to various physiological stimuli. However, the complicated processes governing intracellular Ca²⁺ dynamics within these cell clusters remain largely unknown.
Hypothesis: We hypothesize that specific ion channels and cell-cell junction proteins drive intra- and inter-cellular Ca²⁺ dynamics. We identify key channels and clarify their functional roles in angiotensin II (Ang II)-stimulated JG cells within the native kidney structure.
Methods: We generated mice that express the genetically encoded Ca²⁺ indicator GCaMP6f specifically in JG cells (Ren1^c-GCaMP6f mice) to study Ca²⁺ dynamics. Ex vivo imaging was conducted using kidney slices perfused with varying concentrations of Ca²⁺ and Ang II, along with selective pharmacological inhibitors that target specific Ca²⁺ channels. Furthermore, in vivo Ca²⁺ signaling was examined using multi-photon microscopy in intact kidneys, and acute renin secretion was measured by ELISA.
Results: Ex vivo analysis revealed robust and coordinated intracellular Ca²⁺ oscillations within JG cell clusters following Ang II stimulation, with evident propagation of Ca²⁺ signaling between cells. These oscillations displayed stereotypical burst patterns of Ca²⁺ spikes that were inversely correlated with renin secretion. Pharmacological blockade identified endoplasmic reticulum (ER) Ca²⁺ stores with sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase (Ca²⁺ uptake inlet) and 1,4,5-trisphosphate receptor (Ca²⁺ release), extracellular Ca²⁺ influx via ORAI channels, and gap junction-mediated intercellular communication as primary sources of Ca²⁺ oscillations. Blocking ORAI channels and gap junctions significantly diminished the Ang II-induced suppression of renin secretion (n = 4–5 kidney slices per assay). In line with ex vivo findings, in vivo imaging revealed physiological Ca²⁺ oscillations within native JG cell clusters, which intensified following Ang II administration, concurrently decreasing acute renin secretion (n = 4–7 mice per assay).
Conclusions: Ang II elicits coordinated Ca²⁺ oscillations within JG cell clusters, driven by ER-derived Ca²⁺ release, ORAI channel-mediated extracellular Ca²⁺ influx, and gap junction connectivity. These oscillations collectively suppress renin secretion, underscoring their crucial role in regulating blood pressure and fluid-electrolyte homeostasis.