HOLMAN, J.D.*; HAND, S.C.; Louisiana State University; Lousiana State University: Anoxia Tolerance, Anaerobic Metabolism and Lack of a Mitochondrial Permeability Transition in the Ghost Shrimp, Lepidophthalmus louisianensis.

The ghost shrimp, L. louisianensis, burrows up to meters deep in oxygen-limited marine sediments along the Gulf coast. During low tides these animals are subjected to extended periods of anoxia. Adults of L. louisianensis exhibit a lethal time for 50% mortality (LT₅₀) of 64 h under anoxia at 25� C°. Juveniles have a significantly higher LT₅₀ of 105 h under identical conditions (P = 0.0003). Addition of either an antibiotic cocktail or a fungicide does not extend the survival of adults or juveniles (LT₅₀ of 62 and 100.5 h, respectively). In order to investigate the metabolic impact of prolonged anoxia, we measured whole body lactate levels after 6, 12, 24, 48, and 72 h of anoxia and recorded significant accumulation of this anaerobic end product (ANOVA, P<0.001). Lactate levels were 18.42 � 5.38 μmoles g f.w.^-1 (SD, n = 6) after 6 h and 122.31 � 33.11 μmoles g f.w.^-1 (SD, n = 6) after 72 h. Energized mitochondria isolated from ghost shrimp hepatopancreas possess a pronounced ability to take up exogenous calcium (compared to mitochondria-free controls, ANOVA, P<0.001), as measured by following the external free calcium concentration with the fluorogenic dye Fluo-5N, which cannot penetrate the mitochondrion. Importantly, calcium was not released from the mitochondrial matrix at any level of exogenous calcium tested (up to 1.0 mM, in the presence of 5 mM phosphate). Thus calcium does not stimulate opening of the mitochondrial permeability transition pore, which potentially could help prevent apoptotic and necrotic cell death during extended periods of anoxia. Measurements of adenylate nucleotides are in progress, and the possibility of alternative anaerobic end products is being explored. (Supported by NIH grant 1-RO1-GM0-71345-01).