Ba ²⁺ ‐Induced Vasoconstriction as a Model to Investigate the Dynamin Dependence of Biological Processes Regulating Vascular Tone

Understanding the mechanisms underpinning vascular smooth muscle contraction, which are critical targets for cardiovascular disease treatment, is essential for developing novel therapeutic agents. Recently, the role of mitochondrial fission as a key modulatory event in the vascular contractile process has been questioned. Therefore, the present study, conducted on ex vivo rat aorta rings, aimed to elucidate its role. As mitochondrial dynamics is a Ca²⁺-dependent process, experiments were performed using preparations incubated in a Ca²⁺-free medium, depleted of sarcoplasmic reticulum Ca²⁺ content, and stimulated by Ba²⁺. Contractile responses evoked by Ba²⁺, either alone or in the presence of phenylephrine or (S)-(-)-Bay K 8644, occurred without mitochondrial fission. Furthermore, hallmarks of mitochondrial fusion were observed in rings stimulated by Ba²⁺ alone. The Drp1 inhibitors mdivi-1 and dynasore antagonized Ba²⁺-induced contraction, whereas the dynasore analogue dyngo-4a and the dynamin stimulator ryngo 1-23 synergized with Ba²⁺-induced contraction. All tested compounds, except mdivi-1, induced mitochondrial fission, with particularly pronounced effects observed with dynasore. Similar results were obtained in rings stimulated by Ba²⁺ in the presence of either phenylephrine or (S)-(-)-Bay K 8644. In conclusion, these findings indicate that rat aorta contraction can occur independently of mitochondrial fission. Moreover, Ba²⁺, used in place of Ca²⁺ as a vasoconstricting agent, provides a valuable experimental framework for identifying off-target effects of dynamin modulators.