Meeting Abstract

P1.68  Jan. 4  Control of particle clearance by isolated gills from the clam Mercenaria mercenaria GAINEY, LF, Jr*; GREENBERG, MJ; Univ. of Southern Maine, Portland; C.V. Whitney Lab, Univ. of Florida, St. Augustine gainey@maine.edu

Earlier we showed that the gill muscles in the clam Mercenaria mercenaria contract in response to both 5-hydroxytryptamine (5HT) and dopamine (DA); moreover, these effects are modulated by a nitric oxide (NO) signaling cascade � but only during the winter. The lateral cilia, which pump water through the gills, are also stimulated by 5HT, whereas DA inhibits them. Finding, recently, that isolated gills clear colloidal graphite from seawater, and that clearance rates are measurable, we hypothesized that 5HT would stimulate clearance rates, while DA would inhibit them. 5HT had a biphasic effect on clearance rates: they were increased between 10^-6 and 10^-5 M, but reduced at higher concentrations. During the summer, the gills were less responsive to 5HT: the threshold increased from 10^-6 to 5 x 10^-5 M and, although the rate was still maximal at 10^-5 M, it was still significantly lower than in the winter. L-NAME, an inhibitor of NO synthesis, blocked the effects of 5HT during the winter, but had no effect in summer. Predictably, DA inhibited clearance rates, and the gills were more sensitive to DA in winter than in summer. Microscopic examination of untreated gills revealed no lateral ciliary activity. At 10^-5 M 5HT, which maximizes clearance, the lateral cilia were active and the diameter of the water tubes were increased. Higher concentrations of 5HT contracted the gill musculature, which inhibited the lateral cilia and decreased the diameter of the water tubes. Thus the clearance rates of isolated gills behave in a manner consistent with the pharmacology of the lateral cilia and musculature.