Intravital imaging of afferent arteriole calcium dynamics (692.7)

The afferent arteriole (AA) of the glomerulus is the most critical resistance vessel in the autoregulation of renal blood flow and glomerular filtration rate. Calcium dynamics of the AA, including myogenic contraction and the calcium wave of tubuloglomerular feedback (TGF) have been studied in vitro, however their relevance to in vivo conditions is not known. We aimed to directly visualize the dynamics of intracellular calcium [(Ca2+)i] in cells of the AA in vivo in the intact living kidney. Multiphoton imaging of the kidney was performed <2 weeks after unilateral ureter obstruction (UUO) in mice expressing the genetically encoded calcium indicator GCaMP3 in cells of the renin lineage (Ren1dCre/GCaMP3fl). Myogenic tone of the AA was observed as regularly oscillating AA constrictions, once in every 7.1±0.2 seconds (n=19) associated with minor elevations in AA vascular smooth muscle cells (VSMC) (Ca2+)i. In contrast to the low and even GCaMP3 fluorescence along the length of the AA, high baseline and ∆(Ca2+)i were observed in 1‐2 VSMCs at the glomerular entrance which appeared to function as sphincter cells. Laser‐induced stimulation of macula densa (MD) cell permeability triggered robust, 1.9±0.2‐fold increases in AA VSMC baseline (Ca2+)i and augmented the AA myogenic responses (n=11). Focal MD stimulation triggered a propagating calcium wave along the AA towards proximal segments (with a speed of 6.8±0.9 um/s, n=5) and into the glomerular mesangium (1.2±0.1 um/s). We concluded that AA sphincter cells and MD‐derived signals have the most robust effects on AA (Ca2+)i dynamics and contractility in vivo. Grant Funding Source : Supported by AHA