The effects of temperature, season, and nitric oxide on clearance rates in isolated gills of the heterodont clams Mercenaria mercenaria and Arctica islandica

Abstract

Clearance of colloidal graphite (ml/min g dry weight) was measured in isolated gills treated with 10 −5 M 5-hydroxytryptamine (5HT) in the shallow water eurythermal clam Mercenaria mercenaria and the deeper water stenothermal clam Arctica islandica acclimated to 3 temperatures during the summer and winter. In Mercenaria there were no statistical differences in clearance rates in gills acclimated to 5, 10, and 22 °C during the summer and winter; thus the gills showed perfect temperature compensation (Q 10 = 1). Inhibition of nitric oxide synthesis with L-NAME significantly reduced clearance rates at all three temperatures during the winter but had no effect during the summer. Examination of gills treated with L-NAME and 5HT revealed that the lateral cilia beat at a significantly lower rate than gills treated with 5HT. In Arctica there was no temperature compensation – except at 5 and 10 °C during the winter – as evidenced by Q 10s of 4.0 (winter) and 4.5 (summer) for the temperature range of 0 to 10 °C. In addition, L-NAME had no effect upon clearance during either season. There were no significant differences in the activity of the lateral and frontal cilia, but the interfilament space and the diameters of the water tubes were greater in gills acclimated to 5 °C in comparison to 10 °C during the summer. Arctica gills clear at significantly higher rates than do those of Mercenaria. Examination of gills of both species at 10 °C revealed that the activities of the lateral and frontal cilia are significantly greater in Mercenaria in comparison to Arctica. In contrast the lateral cilia were longer and the interfilament space was larger in Arctica in comparison to Mercenaria.