Meeting Abstract

6.5  Jan. 4  Cell volume stress and respiration of the Antarctic clam Laternula elliptica: implementation of a high-throughput, optical assay of multiple parameters of mitochondrial physiology ULRICH, PN*; MARSH, AG; Univ. of Delaware; Univ. of Delaware pnathanu@udel.edu

Few data are available to describe the sensitivity of Antarctic biota to cell volume stress. We investigated the impact of reduced osmolality on respiration of the Antarctic clam Laternula elliptica at three levels: mitochondria, tissue, and organism. To address mitochondrial respiration, we developed a microplate respirometry technique that can be adapted for measurement of multiple physiological parameters (membrane potential, reactive oxygen production, pH) simultaneously in high throughput with a single fluorometer. Relative to controls (1150 mOsm), low osmolality (635 mOsm) stimulated phosphorylating (state 3) and nonphosphorylating (states 2 and 4) respiration of gill and hepatopancreas mitochondria 1.5 to 3-fold. In contrast to euryhaline bivalves, state 4 respiration was more sensitive to cell volume stress than state 3 respiraiton, depressing the respiratory control ratio (RCR) of gill mitochondria significantly (p = 0.025). Costs of ATP production in L. elliptica gill mitochondria were elevated under low osmolality, as indicated in reduction of ADP:O from 5.62 to 1.99 (p = 0.0012). In low osmolality, membrane potential of gill mitochondria was significantly related to state 2 oxygen consumption. Organismal respiration remained constant when salinity was reduced from 35 to 26 ppt. While isolated gill mitochondria increase respiration in response to lower osmolality, gill tissue respiration dropped threefold at low salinity (p = 0.025). This suggests that L. elliptica gill exerts strong top-down control of mitochondrial respiration. Salinity does not perturb whole organism respiration on the short term, but further research is needed to determine the threshold at which L. elliptica physiology is adversely affected as well as the capacity of the clam to acclimate to reduced salinity.