The Role of Polyamines in pH Regulation in the Extracellular Calcifying Medium of Scleractinian Coral Spats

This study aims to elucidate a novel mechanism for elevating the pH within the calicoblastic extracellular calcifying medium (pH_ECM) of corals and demonstrate the potential contribution of calcifying organisms to CO₂ sequestration. Departing from traditional models that attribute the increase in pH_ECM primarily to H⁺ expulsion via Ca²⁺-ATPase, we emphasize the significant role of polyamines. These ubiquitous biogenic amines conveyed by calicoblastic cells through polyamine transporters demonstrate a remarkable affinity for CO₂. Their ability to form stable carbamate complexes is pivotal in facilitating carbonate ion transport, which is crucial for pH regulation and skeletal structure formation. In this study, a polyamine transporter inhibitor and a polyamine biosynthesis inhibitor in conjunction with the pH-sensitive probe 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) were employed to monitor pH variations. Furthermore, FM1-43FX dye was utilized to delineate the extracellular calcifying medium (ECM), whereas calcein was applied to visualize paracellular gaps and ECM. These methodologies provide profound insights into the intricate structural and functional dynamics of coral spats calcification. Findings suggest a potential reconsideration of established models of marine calcification and highlight the necessity to reassess the role of marine calcifying organisms in the carbon cycle, particularly their influence on CO₂ fluxes.