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Biomedical subjects

J C Ellory

Publications and source records attributed to J C Ellory.

At least 217 records · Page 12Linked to original sources
PubMed1973

The effect of salt adaptation on the permeability and cation selectivity of the goldfish intestinal epithelium.

1. The short-term uptake of Na by the goldfish mucosa was compared using both inulin and choline as markers of extracellular space. The results were virtually identical, the distribution of both choline and inulin increasing rapidly to measure a space at 1 min which then remained nearly constant during a following 4 min incubation.2. Using inulin as space marker, the uptake of various alkali metal cations was determined from a 1 min contact with the mucosa. The relative rates of uptake were Tl > K > Rb > Cs > Na > Li, with a low selectivity ratio, the range of permeabilities being no greater than 5.3. The selectivity sequence was the same in both salt and fresh-water adapted fish. Of the alkali metal cations tested, only Na showed a significantly decreased uptake on adaptation to salt.4. Isolated intestinal preparations from salt-adapted fish showed a reduced short-circuit current compared with fish adapted to fresh water, the values being 12.3 +/- 1.2 and 35.7 +/- 1.5 muA cm(-2) respectively. In both cases the short-circuit current was equivalent to the net transport of Na measured isotopically.5. In Krebs-Henseleit medium, the measured tissue resistance was approximately 100 Omega cm(-2) for both salt and fresh-water adapted fish.6. It is concluded that regulation of cation transport in goldfish intestinal epithelium is specific for Na and mediated primarily through cellular rather than extracellular pathways.

Adaptation, Physiological↗
PubMed1972

Changes in the intestinal transport of sodium induced by exposure of goldfish to a saline environment.

1. The uptake and transflux of sodium by goldfish intestines has been compared under different experimental conditions. Uptake was measured from a 1 min contact of the intestinal mucosa with radioactive sodium chloride solution. Transflux was measured over a period of 2 hr using the everted sac technique.2. Keeping goldfish in saline reduced the transflux of sodium to one quarter the value found for fresh-water fish. The uptake of sodium was halved by this treatment. Cortisol injected previously into saline-adapted fish changed neither the transflux nor the uptake of sodium measured subsequently.3. In fresh-water fish hypophysectomy reduced sodium transflux while leaving the uptake of sodium unchanged. Injection of cortisol restored sodium transflux to control levels without producing any additional effects on the uptake of sodium.4. It is suggested that adaptation to saline involves regulation of sodium movement across the microvillar membrane of the mucosal cell. Cortisol would appear to play no part in this type of regulation.5. The presence of cortisol, or possibly other steroids with similar actions, has however been shown to be essential for the normal operation of sodium transport in this tissue. It is not clear exactly how cortisol exerts this effect. What evidence there is suggests that cortisol exerts a metabolic control rather than changing directly the membrane permeability of the cell.

Adaptation, Physiological↗
PubMed1972

The efflux of magnesium from single crustacean muscle fibres.

1. In the large single muscle fibres from the barnacle Balanus nubilus, the total fibre Mg concentration was estimated as 15.1 m-mole/kg wet wt., of which about 3-3.5 m-mole/kg wet wt. was extracellular. The diffusible Mg, measured by internal sampling, was 11.5 m-mole/kg wet wt., of which at least half may be complexed to larger diffusible molecules. The free ionized Mg level was estimated as < 5 m-mole/kg wet wt.2. The loss of [(28)Mg]MgCl(2) from both Maia and Balanus muscle fibres following axial micro-injection approximated to first-order kinetics. The maximum rate constant for the loss was 1.51 +/- 0.20 (S.E.) x 10(-5) sec(-1) for Balanus (sixty-seven fibres) and 1.06 +/- 0.46 (S.E.) x 10(-5) sec(-1) for Maia (seven fibres) at 20-25 degrees C.3. The calculated Mg efflux was in the range 6-12 p-mole/cm(2).sec based on this rate constant, assuming isotopic equilibration internally and that the surface area of the fibres approximated to that of a simple cylinder. If account was taken of the area of the cleft system the efflux was reduced by about fifteen times.4. The diffusion coefficient for injected (28)Mg was estimated as 2-3 x 10(-6) cm(2) sec(-1), about half the value in free solution. Injections of 2 M-MgCl(2) or 200 mM-EDTA subsequent to the injection of the isotope caused about a 30% reduction in the tracer efflux.5. External application of salines containing 100 mM-Ca or Mg caused a rapid but reversible inhibition of the magnesium efflux. Similar effects were observed with salines containing 32 mM-Co or Mn chlorides or 1-2 mM-La or Gd chlorides. Polyarginine (200 mug/ml.) had no effect.6. The Mg efflux had a Q(10) of 3-4 over the temperature range of about 5-20 degrees C. It was irreversibly inhibited by the sulphydryl reagent NEM (1 mM), but PCMBS (0.2-2 mM) had no effect. Contractile agents (5 mM caffeine or 200 mM-K salines) and a variety of inhibitors of ion movement or active transport had no appreciable effect on the Mg efflux. Lowering the pH of the saline from 7 to 5 produced a 70% reduction in the efflux which was reversible over short periods of application.7. Replacement of external Na, but not Ca or Mg, with Li, choline or sucrose caused a rapid and partially reversible reduction of the Mg efflux, but increasing the internal Na by micro-injection in zero Na salines had no consistent effect. It is suggested that the extrusion of Mg from these muscle cells is largely dependent upon the inward movement of Na.

Animals↗