New calcium signaling mechanisms in the myocytes from small pulmonary veins

Objective: Pulmonary veins (PVs) transport oxygenated blood from the lungs to the left side of the heart. PVs contain myocardial sleeves, which are extensions of the heart muscle into the PVs. It has recently begun to be understood that PV myocytes remodel in pulmonary hypertension (PH). However, compared to pulmonary arteries, signaling mechanisms in PVs remain relatively unexplored. We recently found that the myocyte layer from small PVs expresses functional ryanodine receptors (RyRs). Therefore, the goal of this study was to determine the regulatory mechanisms for RyR activity in small PV myocytes under normal conditions and in PH. We hypothesized that β adrenergic receptors (βAR), L-type Ca 2+ channels (LTCC), and T-type Ca 2+ channels (TTCC) regulate the activity of RyRs in small PV myocytes. Methods: Both Male and Female C57BL6/J mice were used in this study. PH was induced by chronic hypoxia (10% O 2 , 4 weeks) and treatment with the receptor tyrosine kinase inhibitor, SU5416 (20 mg/kg; once a week for three weeks). Mouse intrapulmonary small veins were dissected, incubated with Fluo-4 AM (10 mM) at room temperature for 60 minutes, cannulated on glass micropipettes in a pressure myography chamber, and pressurized to a physiological intraluminal pressure of 5 mm Hg for Ca 2+ imaging. Ca 2+ signals were recorded using a spinning-disk confocal imaging system and analyzed as events/μm 2 /min using custom-designed software. Results: The baseline activity of Ca 2+ signals was completely inhibited by ryanodine (RyR inhibitor, 5 mM), indicating RyR-mediated Ca 2+ release signals. Moreover, the baseline activity of Ca 2+ signals was not different between small PVs from male and female mice. To investigate whether βAR/LTCC/TTCC facilitates RyR Ca 2+ signals in small PVs, the PVs were treated with the following inhibitors: propranolol (bAR, 100 mM), nifedipine (LTCC, 1 mM), or mibefradil (TTCC, 3 mM). Propranolol, nifedipine, and mibefradil inhibited RyR Ca 2+ signals, indicating that βAR, LTCCs, and TTCCs promote RyR Ca 2+ signals in small PV myocytes. We next hypothesized that RyR Ca 2+ signals are altered in a mouse model of PH. Notably, the activity of basal Ca 2+ signals was increased in small PVs from PH mice compared to normal mice, and this activity was inhibited by ryanodine. Conclusions: In conclusion, our findings show that the baseline activity of Ca 2+ signals in the myocyte layer of small PVs at physiological intraluminal pressure represents Ca 2+ release through RyRs. The RyR Ca 2+ signals in PV myocytes are increased by βAR signaling, LTCC and TTCC. Finally, RyR Ca 2+ signals in PV myocytes are increased in PV myocytes in a mouse model of PH. Thus, our results reveal new Ca 2+ signaling mechanisms in PV myocytes. The National Institutes of Health to SKS (HL142808, HL167208, and HL146914) 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.