Simona Salerno‘s PhD work uses two-photon microscopy to assess the electrophysiology of ventricular tissue from small animals.


MAIN RESULTS:

  1. Structural differences between ventricles could explain susceptibility to right ventricular arrythmias in Brugada syndrome.
  2. Infarcted scar tissue displays action potentials with altered electrophysiology.
  3. The novel voltage sensitive dye FluoVolt reduces toxicity and improves fluorescent properties in intact heart preparations.

THESIS DEFENCE:

Thesis: Investigation of cellular and structural basis of cardiac arrhythmias using two-photon microscopy
Candidate: Simona Salerno
Time: May 7, 2020 at 12:15
Place: Online-based solution, due to the covid-19 situation
Link to university website (in Norwegian)


SUMMARY:

(1) Larger intramural clefts between cardiomyocyte layers in the right ventricle compared to the left could be the cause of right ventricular arrhythmias in Brugada syndrome. In the Brugada syndrome, the function of the cardiac sodium channel NaV1.5 is commonly lost in both the left and right ventricle, although arrhythmias preferentially arrise from the right ventricle.

The experiments were conducted on isolated-perfused hearts from wild-type and genetically modified mice, using optical mapping and two-photon microscopy to identify conduction velocities. Cleft differences were similar in both mice groups, but conduction velocities were only impaired during increased pacing of the right ventricle in the genetically modified mouse model. Following acute sodium current inhibition, conduction slowing was also present in right, but not left, ventricular tissue from wild-type mice. Conduction slowing predisposes to functional block and initiation of ventricular arrhythmias.

(2) The ventricular scar has limited, low-amplitude electrical activity following a myocardial infarction. In the border zone between normal and scarred ventricular tissue, action potentials and calcium transients are normal deep down in the tissue, but not in the superficial connective tissue structures. Action potential is significantly slowed in the infarcted zone compared to both the normal zone and the border zone.

The experiments were conducted on ventricular tissue from male rats five weeks after a myocardial infarction due to artery occlusion.

(3) The novel voltage sensitive dye FluoVolt has several advantages over di-4-ANEPPS in deep tissue imaging of rapidly changing electrophysical signals of intact cardiac tissue. In murine hearts, two-photon excitation of FluoVolt reduced episodes of atrio-ventricular block and improved recording of action potentials, compared to loading with di-4-ANEPPS. FluoVolt records membrane potentials by photo-induced electron transfer.


REFERENCES:

(1) Kelly, A., Salerno, S., Connolly, A., Bishop, M., Charpentier, F., Stølen, T., & Smith, G. L. (2018). Normal interventricular differences in tissue architecture underlie right ventricular susceptibility to conduction abnormalities in a mouse model of Brugada syndrome. Cardiovascular research114(5), 724-736.

(2) Ghouri, I. A., Kelly, A., Salerno, S., Garten, K., Stølen, T., Kemi, O. J., & Smith, G. L. (2018). Characterization of Electrical Activity in Post-myocardial Infarction Scar Tissue in Rat Hearts Using Multiphoton Microscopy. Frontiers in physiology9, 1454.

(3) Salerno, S., Garten, K., Smith, G. L., Stølen, T., & Kelly, A. (2019). Two-photon excitation of FluoVolt allows improved interrogation of transmural electrophysiological function in the intact mouse heartProgress in biophysics and molecular biology.

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