The hemolymph CO_2 partial pressure and bicarbonate concentration of the acid-base balance of Mytilus coruscus under resting conditions

We investigated the hemolymph CO_2 partial pressure (Pco_2) and bicarbonate concentration ([HCO_3^–]) 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 CO_2 concentration for this state between 18℃ and 23℃ were 7.568-7.601 and 1.54-1.59 mM/L, respectively. Hemolymph Pco_2 and [HCO_3^–] were calculated using the hemolymph pKapp estimated using the relational expression with temperature. Hemolymph Pco_2 and [HCO_3^–] were 1.77-1.83 torr and 1.47-1.50 mM/L at 18℃ and 23℃. To verify Pco_2 and [HCO_3^–], 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 Pco_2 and [HCO_3^–] were observed. Non-bicarbonate buffer values (ꞵ_NB), which were calculated using the slope of the relational expression between pH and [HCO_3^–] in hemolymph, were 0.42 slykes at 18℃, and 0.54 slykes at 23℃. The hemolymph ꞵ_NB 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.