Mitochondria control IP3-evoked Ca2+ release triggered by voltage-dependent Ca2+ entry in intact resistance arteries

Abstract

The contractility of vascular smooth muscle cells (VSMCs) is a major contributor of vascular tone and blood pressure. In VSMCs, intracellular Ca2+ level determines the contractile activity that generates the force to contract arteries. A major source of Ca2+ is via influx through voltage dependent Ca2+ channels (VDCCs). While mitochondria are now recognised as key regulators of intracellular Ca2+ homeostasis in several cell types, their role in modulating Ca2+ signalling mediated by VDCC in VSMCs is unresolved. Given the potential physiological significance, and unclarified interaction between mitochondria and VDCCs in VSMCs, we hypothesize that mitochondria directly regulate Ca2+ signalling mediated by VDCCs. The interplay between mitochondria and VDCCs was investigated by imaging and analysing intracellular Ca2+ signals in smooth muscle cells in intact arteries from rat mesentery. Depolarization of the plasma membrane potential, by high potassium (20 mM) physiological saline solution, triggered Ca2+ influx through VDCCs and a sustained increase in intracellular Ca2+ on which repetitive Ca2+ oscillations occurred. All Ca2+ signals were abolished by removal of external Ca2+ and by dihydropyridine inhibitors of VDCCs. Significantly, the repetitive Ca2+ oscillations, but not the sustained Ca2+ signals, were blocked by the IP3 receptor inhibitor 2-APB and SERCA inhibitor cyclopiazonic acid. Neither the repetitive Ca2+ oscillations or the sustained Ca2+ signals were altered by the ryanodine receptor inhibitors ryanodine and dantrolene. These results suggest that Ca2+ influx via VDCC triggers Ca2+-induced Ca2+ release at IP3 receptors in intact mesenteric arteries. Depolarization of the mitochondrial membrane potential (ψm), with the uncoupler CCCP or complex I inhibitor rotenone, but not ATP deprivation with the ATP synthesis blocker oligomycin, inhibited VDCC evoked IP3 mediated Ca2+ oscillations but not the sustained Ca2+ signals. Furthermore, in intact arteries, depolarization of ψm directly suppressed inositol triphosphate receptors (IP3Rs) mediated Ca2+ release from the internal Ca2+ store evoked by photolysis of caged IP3. These results suggest that mitochondria regulate Ca2+ release via IP3R triggered by Ca2+ entry via VDCC. In return, Ca2+ entry via VDCCs did not alter ψm, but upregulated ROS production. Together, these results suggest that mitochondria regulate Ca2+-induced Ca2+ release at IP3 receptors triggered by Ca2+ influx via VDCCs but do not directly regulate VDCC activity. British Heart Foundation (RG/F/20/110007; PG/20/9/34859). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.