Calcium Oscillations Within Juxtaglomerular Cell Clusters Control Renin Release.

Background: Juxtaglomerular cells are sensors that control blood pressure and fluid-electrolyte homeostasis. They are arranged as clusters at the tip of each afferent arteriole. In response to decreased blood pressure or extracellular fluid volume, juxtaglomerular cells secrete renin, initiating an enzymatic cascade that culminates in the production of Ang II (angiotensin II), a potent vasoconstrictor that restores blood pressure and fluid-electrolyte homeostasis. In turn, Ang II exerts negative feedback on renin release commensurate with increased intracellular Ca²⁺, preventing excessive circulating renin and hypertension. However, within their native structural organization, the intricacies of intracellular Ca²⁺ signaling dynamics and their sources remain uncharacterized.

Methods: We generated mice expressing the juxtaglomerular cell-specific genetically encoded Ca²⁺ indicator (GCaMP6f) to investigate Ca²⁺ dynamics within juxtaglomerular cell clusters ex vivo and in vivo. For ex vivo Ca²⁺ imaging, acutely prepared kidney slices were perfused continuously with a buffer containing variable Ca²⁺ and Ang II concentrations ±Ca²⁺ channel inhibitors. For in vivo Ca²⁺ image capture, native mouse kidneys were imaged in situ using multiphoton microscopy with and without Ang II and Ang II type-1 receptor blocker losartan administration. ELISA measurements determined acute renin secretion ex vivo and in vivo.

Results: Ex vivo Ca²⁺ imaging revealed that juxtaglomerular cell clusters exhibit robust and coordinated intracellular oscillatory signals with cell-cell propagation following Ang II stimulation. Ang II dose-dependently induced stereotypical burst patterns characterized by consecutive Ca²⁺ spikes, which inversely correlated with renin secretion. Pharmacological channel inhibition identified key sources of these oscillations: endoplasmic reticulum Ca²⁺ storage and release, extracellular Ca²⁺ uptake via store-operated ORAI (Ca²⁺-selective plasma membrane channels involved in store-operated Ca²⁺ entry) Ca²⁺ channels, and intercellular communication through gap junctions. Blocking ORAI channels and gap junctions reduced Ang II inhibitory effect on renin secretion. In vivo Ca²⁺ imaging demonstrated robust intracellular and intercellular Ca²⁺ oscillations within juxtaglomerular cell clusters under physiological conditions, exhibiting spike patterns consistent with those measured in ex vivo preparations. Ang II administration enhanced the Ca²⁺ oscillatory signals and suppressed acute renin secretion, whereas losartan produced inverse effects in vivo.

Conclusions: Ang II elicits coordinated intracellular and intercellular Ca²⁺ oscillations within juxtaglomerular cell clusters, ex vivo and in vivo. The effect is driven by endoplasmic reticulum-derived Ca²⁺ release, ORAI channels, and gap junctions, leading to suppressed renin secretion.