Accumulation and excretion of manganese ion in the kidney of the Mytilus galloprovincialis

Abstract

T1-weighted magnetic resonance imaging (T1w-MRI) was employed to detect the accumulation of manganese ion (Mn2+) in urine in the kidney of Mytilus galloprovincialis, and the longitudinal relaxation rates (1/T1=R1) were measured. When the mussel exposed to seawater containing 10 µM Mn2+, the T1w-MR image intensity and R1 of the kidney, stomach and digestive glands were increased. Mn2+ might be taken into the hemolymph via the gastrointestinal tract, and then filtrated into the pericardium via the auricles. While the image intensity in the pericardium was not affected by manganese, an image intensity enhancement was observed in the distal part of the renopericardial communication canals between the pericardium and kidneys, indicating Mn2+ concentration in the excretion pathway. As the seawater Mn2+ concentration ([Mn2+]SW) was increased from 3 to 50 µM, R1 of the kidney (R1K) were elevated. When the mussels were immersed in 3 - 10 µM [Mn2+]SW for 24 hrs, the Mn2+ concentration in the kidney ([Mn2+]K) increased by 15 fold, compared to the ambient [Mn2+]SW concentration. In the range of [Mn2+]SW from 10 to 50 µM, R1K reached a plateau level that corresponded to 200 µM [Mn2+]K. As [Mn2+]K fell transiently, voluntary excretion of urine from the kidney was assumed. The decreases in intensity were not synchronized between the right and left kidneys, and the closure of the shells might not essential for the urinary excretion. The voluntary excretion suggested an additional explanation for the large variety of metal concentration in the kidneys of the mussel.