Ex Vivo Calcium Imaging of Intact Stellate Ganglion in Angiotensin II-Induced Hypertension

Autonomic dysfunction, including sympathetic hyperactivity, is a common feature of cardiovascular diseases including hypertension. The mechanisms of sympathetic hyperactivity in hypertension are still unclear. Sympathetic nerve firing leads to a rise in intracellular calcium, which then promotes neurotransmitter release. We thus hypothesized that hypertension-induced sympathetic hyperactivity will lead to increased intracellular calcium transients in sympathetic neurons. To test our hypothesis, we developed a novel method for ex vivo calcium imaging of intact stellate ganglia from control and hypertensive mice. We have generated a transgenic mouse model that expresses the genetically encoded calcium indicator, GCaMP6s, in tyrosine hydroxylase (TH)-positive sympathetic neurons (TH GCaMP6s ). TH GCaMP6s male and female mice 12-20 weeks old were implanted with minipumps releasing angiotensin II (AngII, 700ng/min/Kg, N=5) for 7 days to induce hypertension and compared to age and sex-matched non-treated TH GCaMP6s mice (N=6). Tail cuff quantification was used to assess high blood pressure. Calcium imaging experiments were performed using a Nikon Spinning Disk Confocal microscope. We stimulated stellate ganglion explants with nicotine (10 μM) to mimic pre-synaptic transmission and with potassium chloride (KCl, 40 mM) to directly depolarize cells as a positive control for GCaMP6s expression. AngII-treated mice had significantly increased mean arterial pressure 7 days after minipump implantation (p<0.01). Preliminary calcium imaging data showed that nicotine (10 μM) significantly increased peak amplitude and area under the curve in the left but not in the right stellate ganglion neurons from AngII-treated mice when compared to neurons from control animals (p<0.0001; p<0.0001). Time decay of the nicotine peak was decreased in left stellate ganglion neurons from AngII-treated mice (p<0.001), and increased in the right counterpart (p<0.01). Interestingly, when we compared nicotine peaks with KCl peaks, we observed that stellate ganglion neurons from AngII-treated mice showed a higher ratio compared to control (p<0.01), suggesting that neurons from AngII-treated mice are more responsive to nicotine than neurons from control animals. We also observed the presence of higher heterogeneity of intracellular calcium response after nicotine application in stellate ganglion neurons from AngII-treated mice. These data suggest that hypertension leads to elevated intracellular calcium responses which could reflect the sympathetic hyperactivity often associated with this condition. Supported by NIH R01 HL146833 (B.A.H.) This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.