Effects of salinity, temperature and cadmium stress on cadmium -binding protein in the grass shrimp, {\it Palaemonetes pugio}

The combined effects of salinity, temperature and cadmium stress on survival and adaptation through cadmium-binding protein (CdBP) accumulation were studied in the grass shrimp, Palaemonetes pugio. In 96-hour bioassays, shrimp were exposed to zero or one of three levels of cadmium, under one of six different salinity (15, 25, or 35$\perthous$) and temperature (20 or 30$\sp\circ$C) regimes. CdBP concentrations were quantified in survivors from the 24 exposure groups. Salinity and temperature did not affect survivorship unless the shrimp were also exposed to cadmium. Grass shrimp were most sensitive to cadmium at low salinity-high temperature, and least sensitive at high salinity-low temperature. The incidence of cadmium-associated black lesions in gill tissue was influenced by salinity and temperature stress. P. pugio produced a 10,000 dalton metallothionein-like CdBP when exposed to at least 0.1 mg Cd$\sp{2+}$/L for 96 hours. Accumulation of CdBP was increased with increases in the exposure cadmium level, increases in temperature and decreases in salinity, independently and in conjunction with one another. Maximum CdBP concentrations occurred in grass shrimp that survived the salinity-temperature-cadmium conditions creating maximum stress as measured by highest mortality, not necessarily in shrimp exposed to the highest cadmium levels. The potential utility of this method as a monitor of physiological stress in estuarine biota inhabiting metal-polluted environments is discussed. ^

Effect of chitin on {\it Vibrio cholerae}

Chitin, N-acetylglucosamine and crude shrimp shell were found to support growth and survival of non-01 and 01 Vibrio cholerae species in aquatic microcosms. Growth was found to be concentration-dependent when the amount of chitin used was within the range of 0.5 g/L to 5 g/L. Toxigenic strains of V. cholerae retained their ability to produce cholera toxin in bay water with chitin as the sole source of nutrient. The amount of chitin solubilized in bay water was shown to depend on salinity but not pH. The inability of V. cholerae to grow in dilute (10%) sewage is reported, and its bearing on the adequacy of the currently used fecal coliform count as a measure of shellfish and shellfish harvesting water quality is discussed. ^

Role of organic cation transporters in the renal secretion of nucleoside analogs

The mammalian kidney maintains homeostasis of the extracellular environment and eliminates toxic substances from the body, in part via secretion by the organic cation transporters (OCT). Some nucleosides are also secreted by the kidney. Previous work indicated that the deoxyadenosine analog, 2′ -deoxytubercidin (dTub), is secreted by mouse kidney through the OCTs. This study examines the role of OCTs in the renal secretion of dTub and other nucleoside analogs. ^ Using the Xenopus laevis oocyte expression system, the basolateral type rat organic cation transporter rOCT1 was shown to transport dTub and other nucleosides. The positive charged form of dTub (dTub +) appears to be the substrate for rOCT1. Tetraethylammonium (TEA) and dTub competitively inhibit the other's uptake by rOCT1 in a manner consistent with their interaction at a common site. Although 67% homologous with rOCT1, rOCT2 does not mediate the uptake of these nucleosides. Kinetic studies demonstrated the difference in substrate specificity between rOCT1 and rOCT2 to be largely due to a poor affinity of rOCT2 for dTub+. This difference in affinity is located within transmembrane domains 2–7 as determined by chimeric constructs. ^ OCT1 knockout mice were used to evaluate the role of OCT1 in the renal secretion of dTub. No significant difference in tissue distribution and urinary excretion of dTub was observed between the knockout and wild-type mice, indicating that OCT1 is not necessary for the renal secretion of dTub. Apical transporters are postulated to participate in its active secretion. To characterize a possible apical transporter, we screened several renal cell lines for a nucleoside-sensitive OCT. American opossum kidney proximal tubule cells (OK) express a TEA efflux transporter that is inhibited by dTub and other nucleoside analogs. This carrier is metabolic-dependent and distinct from the cloned OCTs to date, i.e. it is sodium- and proton-independent. In conclusion, dTub is a good substrate for OCT1; however, this OCT is not necessary for its renal secretion in mice. The novel TEA efflux transporter identified in OK cells is likely to participate in the renal secretion of dTub and perhaps other nucleoside analogs. ^