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Abstract: SA-OR32

Intravital Imaging of Afferent Arteriole Calcium Dynamics and the Role of Connexin 45

Session Information

Category: Hypertension and CVD

  • 1403 Hypertension and CVD: Mechanisms

Authors

  • Riquier-brison, Anne, University of Southern California, Los Angeles, California, United States
  • Gyarmati, Georgina, University of Southern California, Los Angeles, California, United States
  • Peti-Peterdi, Janos, University of Southern California, Los Angeles, California, United States
Background

The glomerular afferent (AA) and efferent (EA) arterioles are the most critical resistance vessels in the autoregulation of renal blood flow and glomerular filtration rate. Calcium dynamics of vascular smooth muscle cells (VSMC), in part mediated by gap junction communication via connexin 45 (Cx45), are important regulators of AA contractility and myogenic tone. We aimed to study the role of Cx45 in renal hemodynamics in vivo.

Methods

Intravital imaging with multiphoton microscopy (MPM) of renal functional parameters was performed in mice expressing a genetically encoded calcium indicator (GCaMP3 or GCaMP5) in cells of renin lineage with or without connexin 45 knockout (KO). Suramin treatment was used to test the effects of purinergic receptor blockade.

Results

Compared to the uniform upstream AA segment, high baseline and Δ(Ca2+)i were observed in a few AA VSMCs at the glomerular entrance, which appeared to function as sphincter cells. The diameter of the AA (9.24±0.27µm WT, vs. 11.39±0.37µm KO) and EA (7.18±0.36µm WT, vs. 8.58±0.30µm KO) were larger in KO animals, although no difference was found in SBP, snGFR and glomerular diameter. Blood flow in AA was also increased (1.42±0.15µm/ms WT, vs. 2.0±0.12µm/ms KO). AA myogenic tone was visualized 3-4 weeks after unilateral ureteral obstruction (UUO). In WT animals, regular AA contractions were observed uniformly in all AAs with an average frequency of 0.12±0.01 Hz, with large magnitude Δ(Ca2+)i in VSMCs during every contraction (Δ(Ca2+)i = 5564±855 AU). In contrast, KO animals showed highly heterogeneous and irregular AA vascular activity. In those AAs that did exhibit some myogenic tone-like contractions, a higher frequency was observed (0.28±0.02 Hz), however the magnitude of Δ(Ca2+)i in AA VSMCs was much lower than in the WT (Δ(Ca2+)i = 395±249 AU). In both WT and KO animals, treatment with suramin rapidly blocked AA VSMC calcium increases and the myogenic contractions, and the AA became dilated.

Conclusion

AA sphincter cells have robust effects on AA (Ca2+)i dynamics and contractility in vivo, and Cx45 and purinergic signaling are essential components of AA calcium signaling and vascular contractility. Cx45 and purinergic signaling in the AA regulate the myogenic response and renal blood flow, and may be culprit and potential target in vascular pathologies.

Funding

  • NIDDK Support