Mercury in alligators (Alligator mississippiensis) in the southeastern United States.

Mercury methylation may be enhanced in wetlands and humic-rich, blackwater systems that crocodiles and alligators typically inhabit. Given their high trophic level and long life-spans, crocodilians could accumulate significant burdens of Hg. Our objectives were to survey Hg concentrations in alligators from several areas in the southeastern United States to test their utility as sentinels of Hg contamination, to examine relationships among Hg concentrations in various tissues and to look for any differences in tissue Hg concentrations among locations. We measured total Hg concentrations in alligators collected in the Florida Everglades (n = 18), the Okefenokee National Wildlife Refuge, Georgia (n = 9), the Savannah River Site (SRS), South Carolina (n = 49) and various locations in central Florida (n = 21), sampling tissues including blood, brain, liver, kidney, muscle, bone, fat, spleen, claws and dermal scutes. Alligators from the Everglades were mostly juvenile, but Hg concentrations in tissues were high (means: liver 41.0, kidney 36.4, muscle 5.6 mg Hg/kg dry wt.). Concentrations in alligators from other locations in Florida were lower (means: liver 14.6, kidney 12.6, muscle 1.8 mg Hg/kg dry wt.), although they tended to be larger adults. Alligators from the Okefenokee were smallest and had the lowest Hg concentrations (means: liver 4.3, kidney 4.8, muscle 0.8 mg Hg/kg dry wt.). SRS alligators had the greatest size range and intermediate Hg levels (means: liver 14.9, muscle 4.8 mg Hg/kg dry wt.). At some locations, alligator length was correlated with Hg concentrations in some internal organs. However, at three of the four locations, muscle Hg was not related to length. Tissue Hg concentrations were correlated at most locations however, claw or dermal scute Hg explained less than 74% of the variation of Hg in muscle or organs, suggesting readily-obtained tissues, such as scutes or claws, have limited value for non-destructive screening of Hg in alligator populations.

Tissue mercury concentrations in alligators (Alligator mississippiensis) from the Florida Everglades and the Savannah River Site, South Carolina.

Mercury pollution is a serious problem in some areas of the southeastern United States. Due to biomagnification, long-lived predators should have high Hg concentrations in affected areas. American alligators(Alligator mississippiensis) are important predators in many southwestern wetlands, but little information is available on Hg concentrations in this species. We collected tissues from alligators inhabiting two sites in the Everglades, Florida (n = 18) and a manmade reservoir in South Carolina (Par Pond; n = 44), all with documented histories of Hg contamination, and analyzed them for total Hg. Mean concentrations in kidney, liver, muscle, and dermal scutes of alligators from the Everglades (expressed as mg Hg/kg dry mass +/- S.E.M.) were 36.42 +/- 5.23, 41.09 +/- 5.90, 5.57 +/- 0.47, and 5.83 +/- 1.04, respectively. Concentrations in liver, muscle, and scutes from Par Pond alligators were 17.73 +/- 2.56, 4.08 +/- 0.46, and 4.58 +/- 0.63,respectively. Blood from Par Pond alligators contained 2.20 +/- 0.38 mg Hg/kg wet mass. Mercury concentrations did not differ among sexes at any location. Tissue Hg levels did not differ significantly between Everglades locations,but were lower in Par Pond. In Everglades alligators, Hg concentrations in all tissues were positively correlated, as were tissue Hg and total length. Only total length and scute Hg were correlated in Par Pond alligators. Regression revealed a significant relationship between muscle and scute Hg concentrations in Everglades alligators, but not Par Pond alligators. Alligators living in polluted areas can accumulate substantial concentrations of Hg, but relationships among Hg concentrations in specific tissues may vary with location or age and size of the animals sampled.

Cloned human aquaporin-1 is a cyclic GMP-gated ion channel.

Aquaporin-1 (AQP1) is a member of the membrane intrinsic protein (MIP) gene family and is known to provide pathways for water flux across cell membranes. We show here that cloned human AQP1 not only mediates water flux but also serves as a cGMP-gated ion channel. Two-electrode voltage-clamp analyses showed consistent activation of an ionic conductance in wild-type AQP1-expressing oocytes after the direct injection of cGMP (50 nl of 100 mM). Current activation was not observed in control (water-injected) oocytes or in AQP5-expressing oocytes with osmotic water permeabilities equivalent to those seen with AQP1. Patch-clamp recordings revealed large conductance channels (150 pS in K(+) saline) in excised patches from AQP1-expressing oocytes after the application of cGMP to the internal side. Amino acid sequence alignments between AQP1 and sensory cyclic-nucleotide-gated channels showed similarities between the cyclic-nucleotide-gated binding domain and the AQP1 carboxyl terminus that were not present in AQP5. Competitive radioligand-binding assays with [(3)H]cGMP demonstrated specific binding (K(D) = 0.2 microM) in AQP1-expressing Sf9 cells but not in controls. These results indicate that AQP1 channels have the capacity to participate in ionic signaling after the activation of cGMP second-messenger pathways.