The Acid-base Balance of the Hemolymph of the Hard Clam (Meretrix lusoria) is Affected by Aerial Exposure and Cellular Hypoxia-inducing Factors

Abstract

After 1 min aerial exposure, the hemolymph pO2 of hard clams (Meretrix lusoria) was reduced from 23.8 mmHg initially to 18.3 mmHg at 15℃, while it significantly decreased from 27 mmHg initially to 14 mmHg at 30℃. This rapid decline in the hemolymph pO2 of hard clams may have been due to a low concentration of oxygen carriers in the hemolymph. Indeed, the hemoglobin in hemolymph of hard clams was not detectable, while a value of 0.075 mM hemocyanin in the hemolymph was obtained. After clams were exposed to Mg(superscript +2)-free artificial seawater for 10 h, the hemolymph pO2 of significantly dropped from 24 to 13 mmHg. However, the hemolymph pCO2 and HCO(superscript -)3increased from 4.8 mmHg and 4.3 mmol/l initially to 10 mmHg and 9.9 mmol/l at 10 h of exposure and then decreased to 6.5 mmHg and 7.6 mmol/l at 48 h of exposure, respectively. Potassium reduced the hemolymph pO2 and increased the hemolymph pCO2, while it had no influence on hemolymph pH or HCO(superscript -)3 during the experiment. KCN persistently decreased the hemolymph pO2, while its only effect on the hemolymph pH and HCO(superscript -)3 occurred in the early phase of exposure.