The hemolymph CO2 partial pressure and bicarbonate concentration of the acid–base balance of Mytilus coruscus under resting conditions

We investigated the hemolymph CO2 partial pressure (Pco2) and bicarbonate concentration (HCO3 – ) of the acid–base balance of Mytilus coruscus under resting conditions. Hemolymph collected from the adductor muscle was subjected to the following measurements. Mean values for hemolymph pH and total CO2 concentration for this state between 18°C and 23°C were 7.568-7.601 and 1.54-1.59 mM/L, respectively. Hemolymph Pco2 and HCO3 – were calculated using the hemolymph pKapp estimated using the relational expression with temperature. Hemolymph Pco2 and HCO3 – were 1.77-1.83 torr and 1.47-1.50 mM/L at 18°C and 23°C. To verify Pco2 and HCO3 – , the values were calculated using pKapp obtained by in vitro method (tonometry). Despite the different determination methods, no statistical difference in the obtained values of Pco2 and HCO3 – were observed. Non-bicarbonate buffer values (ꞵNB), which were calculated using the slope of the relational expression between pH and HCO3 – in hemolymph, were 0.42 slykes at 18°C, and 0.54 slykes at 23°C. The hemolymph ꞵNB of M. coruscus was in the range of other bivalves, and the hemolymph buffer capacity of the non-bicarbonate buffer system would reflect the Mitilid species.