Search PubMed⌕ Search

Biomedical subjects

J B Steen

Publications and source records attributed to J B Steen.

33 records · Page 2Linked to original sources
PubMed1975

The permeability of fish gills with comments on the osmotic behaviour of cellular membranes.

The permeability of eel gills to ions, lipid-soluble and -insoluble substances has been measured under steady-state conditions. The results obtained support the multi-pathway model for transcapillary transport (Stray-Pedersen and Steen 1975). The gills are 25 times more permeable to THO than to Na+ or K+. Metabolic inhibitors do not affect the transfer of substances across the gills. Exposure to EDTA or MS-222 changes the permeability properties to resemble those of an aquous barrier. The gills are 10 times less water permeable than the capillaries of the rete mirabile.

Animals↗
PubMed1975

Regulation and grinding ability of grit in the gizzard of Norwegian willow ptarmigan (Lagopus lagopus).

Fluctuations in grit composition in the gizzards of willow ptarmigans and the grinding ability of various grit assortments from wild ptarmigans were examined. We confirmed reports of other investigators that larger, fewer and rounder stones were present in the winter than in the autumn. Experiments showed that ptarmigans prefer stones with diameters between 2-5 mm. Birds on a constant diet maintained a constant stone intake throughout the year. The composition of gizzard grit was influenced by the availability of stones as well as of the type of food the ptarmigans ate. Using an artificial gizzard, grit from birds shot during the autumn was found to be a more efficient grinding material than grit from winter birds. We suggest that other functions than grinding, such as supplying minerals, may be equally important functions of the grit.

Animals↗
PubMed1969

The rate of the root shift in eel red cells and eel haemoglobin solutions.

1. We have measured the rate of the exchange of O(2) between eel red blood cells and their suspending fluid in a modified Hartridge-Roughton continuous-flow rapid-reaction velocity apparatus using an oxygen electrode to follow the progress of the reaction.2. The half-times for the uncomplicated oxygenation and deoxygenation reactions in red cells at 24 degrees C were approximately 0.025-0.08 sec.3. The rate of the Root shift in cell suspensions varied widely, depending on the initial condition of the CO(2)-bicarbonate buffer system in the suspending fluid, with the rate of oxygenation or deoxygenation of the intracellular haemoglobin as an upper limit.(a) The most rapid Root shift was produced by a change in extracellular P(CO2) with minimal contributions from CO(2) hydration-dehydration reactions in the suspending fluid or from ion exchanges across the membrane, and had a half-time as short as 0.040 sec.(b) The slowest Root shift was produced by an increase in the extracellular lactic acid concentration in the absence of any form of CO(2) or in the presence of acetazolamide. This process is presumed limited by the rate of H(+) or OH(-) transfer across the membrane and had a half-time in excess of 10 sec.(c) The Root off-shift produced by an increase in P(CO2) plus a decrease in extracellular pH showed no significant trend as temperature was lowered from 30 degrees to 11 degrees C.(d) The Root on-shift produced by a decrease in P(CO2) and increase in extracellular pH had a half-time of 3 sec at 30 degrees C, 9 sec at 24 degrees C and 20 sec at 11 degrees C. These changes appeared limited by the uncatalysed rate of extracellular CO(2) hydration.4. Root off- and on-shifts in cell haemolysates at 24 degrees C, produced predominantly by changing pH but with unavoidable subsequent readjustments of the CO(2)-bicarbonate buffer systems, had an initial rapid phase with half-times as low as 0.01 sec. However, the curves were not monotonic, although they became so in the presence of carbonic anhydrase, indicating partial rate limitation by CO(2) reactions.

Acetazolamide↗
PubMed1968

The mechanism of oxygen concentration in the swim-bladder of the eel.

1. The P(O2) of venous blood from the active swim-bladder of the eel was shown to decrease with distance from the exit of the rete. This systematic change did not occur in non-secreting bladders, nor during conditions where exchange in the rete had been abolished.2. The observed change in post-rete venous P(O2) has the same rate constant as the Root-on shift.3. These findings modify the accepted model for counter-current multiplication of O(2) in the swim-bladder system by introducing rate constants for diffusion and action of acid in the rete.4. The part played by the assumed impermeability to acid of the arteriovenous partition of the rete is in the modified model replaced by the slow Root-on shift.5. The modified model contradicts the Kuhn model in that extraction of O(2) from blood is decreased at low flow and that at normal flow conditions part of the lactic acid produced can be re-used.6. Similar modifications are indicated in the model for concentration of inert gases.

Air Sacs↗
PubMed1968

Rate limiting processes in the Bohr shift in human red cells.

1. The rates of the Bohr shift of human red cells and some of its constituent reactions have been studied with a modified Hartridge-Roughton rapid reaction apparatus using an oxygen electrode to measure the progress of the reaction.2. The rate of the Bohr shift was compatible with the hypothesis that the transfer of H(+) across the membrane by means of CO(2) exchange and reaction with buffers is generally the rate-limiting step.(a) When the Bohr off-reaction was produced by a marked increase in P(CO2) around the cells, the half-time at 37 degrees C was 0.12 sec. In this case CO(2) was available initially to diffuse into the cells, the process being predominantly limited by the rate of intracellular CO(2) hydration.(b) When the Bohr off-shift was produced by an increase of [H(+)] outside the cell, P(CO2) being low and equal within and outside the cells, the half time became 0.31 sec. In this case, even at the start, the H(2)CO(3) formed by the almost instantaneous neutralization reaction of H(+) and HCO(3) (-) had to dehydrate to form CO(2) and this in turn had to diffuse into and react within the red cell before the [HbO(2)] could change. When a carbonic anhydrase inhibitor was added to slow the CO(2) reaction inside the cell, the half-time rose to 10 sec.(c) The Bohr off-shift in a haemolysed cell suspension produced by an increase in P(CO2) appeared to be limited by the rate at which the CO(2) could hydrate to form H(+).3. The Bohr off-shift has an average Q(10) of 2.5 between 42.5 and 28 degrees C with an activation energy of 8000 cal.4. The pronounced importance of the CO(2)-bicarbonate system for rapid intracellular pH changes is discussed in connexion with some physiological situations.

Acetazolamide↗