Meeting Abstract

P3.73  Tuesday, Jan. 6  Nitric oxide is the agent of seasonal temperature compensation of clearance rates in isolated gills of Mercenaria mercenaria GAINEY, L.F., JR*; GREENERG, M.J.; Univ. of Southern Maine, Portland; C.V. Whitney Lab., Univ. of Florida, St. Augustine gainey@maine.edu

The gills of the clam Mercenaria mercenaria contain a seasonally expressed nitric oxide (NO) signaling cascade. In gills isolated in winter, NO potentiates the effects of 5HT on both muscle contraction and the rate of particle clearance, but NO has no effect during the summer. We wondered whether NO acts by mitigating the effects of lower temperatures on clearance rates during the winter. To test this hypothesis, we acclimated clams to 5, 10 and 22 C during the summer and the winter. One set of isolated gills was exposed to 10^-5 M 5HT to maximize the rate of clearance, and the other set to both 5HT and 10^-5 M L-NAME, the latter to inhibit the synthesis of NO. A three-way full factorial ANOVA, with season, temperature and treatment (5HT or 5HT and L-NAME) as the main effects, revealed that only season and season*treatment were significant. Post hoc analysis of the season*treatment means revealed that: 1) temperature had no effect on clearance rates in either season; and 2) L-NAME had no effect during the summer, when the NO signaling cascade is not functional; but 3) during the winter and at all temperatures, L-NAME significantly reduced clearance rates. These results support our hypothesis that NO is the agent of seasonal temperature compensation of clearance rates.