Meeting Abstract
P3.1 Tuesday, Jan. 6 Nitric Oxide Synthase Activity Correlates with Hemoglobin Content in Antarctic Notothenioid Fishes BEERS, J. M.*; SIDELL, B. D.; University of Maine, Orono; University of Maine, Orono jody.beers@maine.edu
Antarctic icefishes are the only known adult vertebrates to lack the circulating oxygen-binding protein, hemoglobin (Hb). In addition to carrying oxygen, Hb is the primary reactant in degradation of the bioactive molecule, nitric oxide (NO). We thus expect NO to be degraded at a slower rate in Hb-lacking icefish than in Hb-expressing notothenioids, leading to higher steady-state levels of NO in the former group. Data from our laboratory support this prediction. Steady-state concentration of NO, however, reflects a balance between rates of synthesis and degradation. To evaluate the role of NO synthesis, we measured catalytic activity of the enzyme responsible for NO production, nitric oxide synthase (NOS). A 14C-radiochemical assay was used to determine NOS activity in different tissues of both white- and red-blooded notothenioids. In brain tissue, NOS activity (pmol min-1 g wet wt.-1) is greatest in Hb-expressing Notothenia coriiceps (160 11) and lowest in Hb-lacking Chaenocephalus aceratus (96 10). Red-blooded Parachaenichthyes charcoti, with Hb levels lower than N. coriiceps, displays NOS activity intermediate to that of N. coriiceps and C. aceratus (116 7). Total NOS activity in cardiac tissue is significantly lower than in brain tissue, but shows the same trend between white- and red-blooded species, with greatest activity seen in those species expressing Hb (C. aceratus 0.50 0.17; N. coriiceps 2.93 1.36). Our results suggest that NOS activity in icefishes is downregulated in response to high levels of NO. Therefore, Hb-lacking notothenioids may decrease NO production to compensate for slow degradation of this signaling molecule. We currently are examining tissue-specific distribution of NOS isoforms in these animals. Supported by NSF grants ANT 04-37887 and 07-39637.
