Epithelial cells of the gut, antennal glands, integument, and gills of crustaceans regulate the movements of ions into and across these structures and thereby influence the concentrations of ions in the hemolymph. Specific transport proteins serving cations and anions are found on apical and basolateral cell membranes of epithelia in these tissues. In recent years, a considerable research effort has been directed at elucidating their physiological and molecular properties and relating these characteristics to the overall biology of the organisms. Efforts to describe ion transport in crustaceans have focused on the membrane transfer properties of Na+/H+ exchange, calcium uptake as it relates to the molt cycle, heavy metal sequestration and detoxification, and anion movements into and across epithelial cells. In addition to defining the properties and mechanisms of cation movements across specific cell borders, work over the past 5 yr has also centered on defining the molecular nature of certain transport proteins such as the Na+/H+ exchanger in gill and gut tissues. Monovalent anion transport proteins of the gills and gut have received attention as they relate to osmotic and ionic balance in euryhaline species. Divalent anion secretion events of the gut have been defined relative to potential roles they may have in hyporegulation of the blood and in hepatopancreatic detoxification events involving complexation with cationic metals.

Diapausing embryos of the annual killifish Austrofundulus limnaeus have the highest reported anoxia tolerance of any vertebrate and previous studies indicate modified mitochondrial physiology likely supports anoxic metabolism. Functional mitochondria isolated from diapausing and developing embryos of the annual killifish exhibited VO(2), respiratory control ratios (RCR), and P:O ratios consistent with those obtained from other ectothermic vertebrate species. Reduced oxygen consumption associated with dormancy in whole animal respiration rates are correlated with maximal respiration rates of mitochondria isolated from diapausing versus developing embryos. P:O ratios for developing embryos were similar to those obtained from adult liver, but were diminished in mitochondria from diapausing embryos suggesting decreased oxidative efficiency. Proton leak in adult liver corresponded with that of developing embryos but was elevated in mitochondria isolated from diapausing embryos. In metabolically suppressed diapause II embryos, over 95% of the mitochondrial oxygen consumption is accounted for by proton leak across the inner mitochondrial membrane. Decreased activity of mitochondrial respiratory chain complexes correlates with diminished oxidative capacity of isolated mitochondria, especially during diapause. Respiratory complexes exhibited suppressed activity in mitochondria with the ATP synthase exhibiting the greatest inhibition during diapause II. Mitochondria isolated from diapause II embryos are not poised to produce ATP, but rather to shuttle carbon and electrons through the Kreb's cycle while minimizing the generation of a proton motive force. This particular mitochondrial physiology is likely a mechanism to avoid production of reactive oxygen species during large-scale changes in flux through oxidative phosphorylation pathways associated with metabolic transitions into and out of dormancy and anoxia.

Two inbred mouse strains, C57BL/6J (B6) and DBA/2J (D2), were evaluated for effects of ethanol on thermoregulation. Continuous recording of core temperature (Tc) from undisturbed animals at an ambient temperature (Ta) of 27 degrees C indicated Tc was similar for both strains during active (approximately 38.0 degrees C) and inactive (approximately 36.7 degrees C) periods. Ethanol-injections of 1.5, 2.5, 3.5, and 4.5 g/kg in an environment where Ta rose and fell at 6-min intervals, reaching extremes of 14 and 42 degrees C, produced dose-dependent falls in Tc for both strains. The changes in Ta produced fluctuations in Tc under all conditions. The amplitude of these fluctuations in Tc was used as a measure of physiological disruption. Dose-dependent increases in disruption were found for both strains. At a constant 26 degrees C Ta, ethanol produced dose-related increases in tail temperature. Responses after ethanol administration were different for B6 and D2 mice. The results indicate regulated temperature is similar for B6 and D2 strains. Regulated temperature is decreased more by ethanol for B6 mice, whereas disruption of thermoregulation by ethanol is greater for D2 mice.

The ef fects ql ionic and/or osmotic change on skeletal muscle mitochondrial per formance were inuestigated. Two substrates, pyruvate and glutamate, and varia tion in osmotic pressure from 205 to 360 mosm in KCl or mannitol/sucrose media had no effect on maximal respiratory rate (state 3) or coupling (respiratory con trol ratio) in either species. Ouer an equivalent range of osmolalities associated with dehydration, organismic maximal 02-consumption rates are severely dimin ished with increasing osmolalities. The data do not support a mitochondria/limit to organismic 02 consumption under dehydration. There were interspecies diff er ences in state 3 respiration and coupling that were similar to differences noted in mitochondria isolated from fish red and white muscle, with toad mitochondria behauing more like red muscle and frog mitochondria behaving more like white muscle.

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In recent years, an electrogenic 2Na+/1H+ antiporter has been identified in a variety of invertebrate epithelial brush-border membranes of gut, kidney and gill tissues. The antiporter differs significantly in its physiological properties from the electroneutral 1Na+/1H+ antiporter proposed for vertebrate cells. In all invertebrate cells examined, the antiporter displayed a 2:1 transport stoichiometry, responded to an induced transmembrane potential and exhibited a high binding affinity for the divalent cation Ca2+, which acted as a competitive inhibitor of Na+ transport. A monoclonal antibody specific for the crustacean electrogenic antiporter inhibited 2Na+/1H+ exchange, but was without effect on Na(+)-dependent D-glucose transport. Immunoreactivity was localized at hepatopancreatic brush-border and vacuolar membranes, antennal gland coelomosac podocytes and posterior gill epithelial cells-all locations were published reports described unique cation exchange kinetics. Significant fractions of Ca2+ transport into invertebrate cells across brush-border membranes occurred by an electrogenic, amiloride-sensitive exchange process, probably by the 2Na+/1H+ antiporter, and this transport was markedly inhibited by exogenous zinc and cadmium. A recently identified electroneutral, amiloride-sensitive, hepatopancreatic epithelial basolateral Na+/H+ antiporter was uninfluenced by the brush-border monoclonal antibody, exhibited an apparent 1:1 transport stoichiometry and possessed a minimal divalent cation specificity. Calcium transport at this epithelial pole occurred by the combination of a Ca2+/Na+ antiporter, an ATP-dependent Ca(2+)-ATPase and a verapamil-sensitive calcium channel. These crustacean brush-border and basolateral transporters may play significant roles in calcification and heavy metal detoxification.

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