P.J. Bentley

Influx of zinc by channel catfish (Ictalurus punctatus) : uptake from external environmental solutions

1. Channel catfish (Ictalurus punctatus) take up zinc (measured with 65Zn) from external ambient solutions in a concentration dependent manner. At a concentration of 10(-6)M Zn, this uptake is equivalent to 0.4% of the total body Zn each day. 2. Zinc influx was increased by external acid conditions (decreasing pH from 7.3 to 5). 3. Elevated Ca2+ and Cd2+, but not Al3+, concentrations markedly decreased the uptake of Zn. 4. These observations may be relevant to circumstances that occur under natural conditions, and influence the zinc nutrition and toxicity of the fish.

Electrical PD, short-circuit current and fluxes of Na and Cl across avian intestine.

Summary1.In vitro measurements were made of transmural potential difference (PD), short-circuit current (Isc), resistance and unidirectional fluxes of22Na and36Cl across the duodenum, jejunum, ileum and colon of normal sodium-replete domestic fowl (Gallus domesticus).2.The PD ranged from about 1 mV across the duodenum to 8mV across the colon while theIsc was, respectively, 2.8 and 64 μA · cm−2. The jejunum and ileum exhibited values between these extremes.3.Unidirectional fluxes (under short-circuit conditions) of Na and Cl were lowest across the duodenum where there was no evidence of active transport of these ions. Unidirectional fluxes of Na and Cl were less across the jejunum than across the ileum or colon. A net active transport of Na (but not Cl) was observed in the ileum (=106% of theIsc) and colon (=50% ofIsc).4.The possible physiological significance of these observations in the domestic fowl are discussed and are compared to that of a mammal, the rabbit.

Accumulation of cadmium by the eye with special reference to the lens

Subcutaneously administered Cd2+ (in vivo) was accumulated in the eyes of rabbits. The concentration was greatest in the iris-ciliary body, followed by the retina, cornea, and lens. It was also present in the vitreous humor, but was not detectable in the aqueous humor. Cd2+ in the bathing medium in vitro was toxic to the lens (tissues gained Na and lost K) at 10(-3) M, for 24 hr incubation, or 10(-5) M, for 7 days. Cadmium-109 was gradually accumulated by the lens in vitro (the process may be saturable), but with 10(-7) M Cd in the medium (similar to the vitreous in Cd-treated rabbits) 100 times less was taken up in 24 hr than in the 28-day in vivo experiments. Cadmium-109 in vitro was almost confined to the outer 30 to 50% of the lens tissue. Cadmium-109 was able to reenter the bathing medium, and its efflux was not changed by the presence of external Cd, suggesting that substantial specific binding was not occurring. Efflux could be reduced by lanthanum so that it may follow pathways similar to those used by Ca and Zn.

Accumulation of cadmium by channel catfish (ictalurus punctatus): Influx from environmental solutions

1. The accumulation of cadmium (Cd) from external environmental solutions was measured in channel catfish (Ictalurus punctatus) with the aid of 109Cd and by direct analysis of tissues. 2. Acute uptake (with 109Cd) was concentration dependent and was increased by changing the external pH from 7.3 to 5.0 and decreased by raising the Ca concentration from 0.1 mM to 3.0 mM. 3. The presence of external Zn did not change the uptake of the Cd. 4. In chronic 7-day experiments, fasted catfish were found to accumulate the toxic metal in their liver and kidneys from external media with Cd concentrations as low as 10(-9) M (about 0.1 microgram/l). 5. Concentrations were greater in the kidneys than the liver. 6. Detectable amounts of Cd (less than 0.03 microgram/g net wt) were not found in muscle in this time at external concentrations of Cd less than 10(-5) M (less than 1.0 mg/l).

Tissue distribution of subcutaneously administered aluminum chloride in weanling rabbits

The purpose of our investigation was to determine blood and tissue levels of aluminum (Al) in normal young rabbits. Furthermore, we wished to determine tissue distribution and accumulation of Al as related to its blood concentration in Al-dosed rabbits. The levels of Al accumulated were determined in different tissues of growing rabbits after continuous subcutaneous administration of Al chloride (3.78 mg/d) for 28 d. No signs of toxicity were apparent from comparisons of hematocrit or weight gain between control and Al-dosed rabbits. The largest concentration of the Al was observed in bone, which was also found to have the highest levels in the control rabbit tissues. Following bone, the experimental animals showed the greatest increase of Al levels in kidney cortex, kidney medulla, liver, testes, skeletal muscle, heart, brain white matter, and brain hippocampus, in that order. No significant difference was found in brain grey matter between control and experimental animals. As the brain tissue of the Al-treated animals had the lowest Al level of the tissues measured, it appears that there is a partial blood-brain barrier to entry of Al.

A high-affinity zinc-binding plasma protein in channel catfish (Ictalurus punctatus).

1. Channel catfish (Ictalurus punctatus) have a remarkably high concentration of zinc (Zn) in their blood serum, about 20 micrograms/ml. However, compared to mammals, the concentrations of Zn in their tissues are not remarkable. The serum Zn is dialyzable against a solution containing 1 mM EDTA. 2. Following separation of serum proteins by gel-filtration most of the Zn was recovered in a fraction with the same peak volume of elution for the Zn and protein concentrations and having a molecular weight similar to bovine serum albumin. 3. Binding of Zn to such sites was not changed by Cu2+, Cd2+, Ca2+, or La3+. N-ethylemaleimide (NEM) appeared to decrease binding slightly. 4. Equilibrium dialysis with a Scatchard plot analysis of these data suggested that a single set of binding sites was present on the protein(s) with KD of 2 x 10(-5) M. There were binding sites for 35 x 10(-8) M Zn/mg protein. 5. Parallel equilibrium dialysis measurements using human, rabbit and chicken albumins indicated that the catfish serum protein(s) had a much higher affinity and binding capacity for Zn than the albumins in these species. 6. The catfish Zn serum-binding protein may be an albumin. The possible physiological significance of such a serum protein in freshwater fish is discussed.

Exchanges of lead in vitro by the rabbit crystalline lens.

Lead (using 203Pb as a tracer) is accumulated by rabbit lenses in vitro. This accumulation was time and concentration-dependent and could be inhibited by La3+. The results suggest that the process involves diffusion, but an interaction with anionic sites on the cell membranes may be involved. Tissue saturation concentrations of Pb were six times greater at 10(-5) M Pb as compared with 10(-6) M suggesting that the affinity of the metal ion for tissue ligands is quite low, but comparable to that in other tissues. Loss of accumulated 203Pb was slightly increased by La3+ suggesting that some binding to the plasma membrane is occurring. The thiol agent dithiothreitol considerably enhanced loss of 203Pb. Exposure of lenses to 10(-4) M Pb for 2 days resulted in an increased accumulation of sodium and loss of potassium, but lenses remained viable in 10(-5) M Pb for at least 3 days.

Unidirectional fluxes of na+, cl−1 and water in fingerling channel catfish, ictalurus punctatus

Abstract 1. 1. The influx of Na+ and Cl−(as 22Na+ and 36Cl−1) was measured in fingerling channel catfish (Ictalurus punctatus) and was found to be equivalent in a 7–8 g fish to about 20 and 40%, respectively, each day of their total body Na or Cl. In the smallest fish (l g), the rate of flux was 3–4 times as great as in larger (15g) ones. 2. 2. Unidirectional flux of water (as efflux of 3H-water) was very rapid, equivalent to about 3 times the total body water each hour. 3. 3. Drinking was relatively small equivalent to about 2.5% of the body weight each day (6% at pH 5) and so contributed little to the above fluxes, which presumably mainly occurred across the gills and possibly the skin. 4. 4. Influx of Na+ was reduced when the Ca2+ concentration was increased from 0.1 to 3 mM. Changes of pH between 8.3 and 5 and the presence of 0.01 mM A13+ such as may result from “acid rain” did not change Na influx. 5. 5. Efflux of Na+ was increased when the pH was decreased from 7.3 to 5, but neither Ca2+ (3 mM) nor Al3+ (0.01 mM at a pH of 5) had a significant effect. 6. 6. The unidirectional flux of water was reduced by 0.01 mM Al3+ at pH 5, but it was unchanged by a pH of 5 alone or 3 mM Ca2+.

Avian colonic ion transport: effects of corticosterone and dexamethasone.

Summary1.Corticosterone, a natural corticosteroid hormone in birds, when injected into domestic fowl (Gallus domesticus) (2000 μg·kg−1, 4–5 h before experiment) increases both the basal Isc (short-circuit current) and amiloride-sensitive Isc as well as the PD across the colon in vitro. Dexamethasone, a synthetic analogue (650 μg·kg−1, 4–5 h before experiment) also increases the basal and amiloride-sensitive Isc as well as PD in these preparations.2.In marked contrast, longer term injection or infusion of dexamethasone (650 μg·kg−1) for 3 or more days caused a decline in basal Isc and PD (the PD often reversed with the serosal side becoming electronegative) and a drop in resistance. However in these preparations, the amiloride-sensitive Isc was significantly elevated which could be accounted for by an increase in net Na flux.3.No significant change occurs in net flux of Cl or K although unidirectional fluxes in both directions were increased for both ions in birds given dexamethasone for 3 days.4.A disparity between the basal Isc and the amiloride-sensitive Isc appeared in these preparations from dexamethasone injected birds reflecting the transport of other ions, possibly HCO3− or H+. The possible role of corticosterone in mineral metabolism of birds is discussed.

Ocular chrysiasis: accumulation of gold in the rabbit eye

Gold entered the eye and was accumulated in the aqueous humor, iris-ciliary body, and cornea (measured by flameless atomic absorption spectroscopy) of rabbits given gold sodium thiomalate by subcutaneous infusion for 4 weeks. It was not detected following such exposure in the vitreous humor, lens or retina. The concentration of gold in the cornea was quite high, about 25% of that in the liver. The concentration in the aqueous humor was only about 2.5% of that in the plasma, which is similar to the fraction of gold (5%) that is not bound to plasma proteins.