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First published online June 29, 2007
Journal of Experimental Biology 210, 2518-2525 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.005637
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Seasonal control of particle clearance by isolated gills from the clam Mercenaria mercenaria

Louis F. Gainey, Jr

Department of Biological Sciences, The University of Southern Maine, Portland, ME 04104, USA

e-mail: gainey{at}maine.edu

Accepted 2 May 2007

Pieces of gill isolated from the clam Mercenaria mercenaria clear colloidal graphite from seawater, and the clearance rates are measurable. 5-Hydroxytryptamine (5-HT) had a biphasic effect on clearance rates: concentrations from 10–6 to 10–5 mol l–1 5-HT increased clearance, but higher concentrations reduced it. During the summer, the gills were less responsive to 5-HT: the threshold increased from 1x10–6 to 5x10–6 mol l–1, and although the rate was still maximal at 10–5 mol l–1, it was significantly lower than the maximal rate in the winter. At 10–5 mol l–1 5-HT, which maximized clearance, the lateral cilia were active, the interfilament space decreased and the diameter of the water tubes increased. Higher concentrations of 5-HT contracted the gill musculature, which inhibited the lateral cilia, decreased the interfilament space even more and decreased the diameter of the water tubes. The nitric oxide (NO) generator DEANO stimulated clearance in the winter but had no effect during the summer. L-NAME, an inhibitor of NO synthesis, diminished the effect of 5-HT during the winter but was ineffective during the summer. The diminished response to 5-HT of winter gills treated with L-NAME was statistically equal to the response of the gills to 5-HT during the summer. Dopamine (DA) inhibited clearance, and the gills were more sensitive to DA in winter than in summer. Microscopic examination of untreated gills revealed little or no lateral ciliary activity, and clearance was minimal. Thus, clearance rates of isolated gills behave in a manner consistent with the seasonality and pharmacology of the lateral cilia and branchial musculature.

Key words: clearance, gill, clam, 5-HT, 5-hydroxytryptamine, Mercenaria mercenaria






© The Company of Biologists Ltd 2007