Biomedical subjects

K L Shephard

Publications and source records attributed to K L Shephard.

7 recordsLinked to original sources

PubMed1995

State of airway surface liquid on guinea pig trachea.

Two preparations of the guinea pig trachea have been examined: an isolated preparation and a preparation in vivo, both exposed to air on the mucosal surface. Ion-selective microelectrodes have been used to measure Na (alpha Na) and K activities (alpha K) in airway surface liquid (ASL) while airflows tending either to evaporate or to condense water were applied. Other variables measured included ASL depth and transepithelial potential difference (TEPD). In isolated preparations, condensation did not progressively alter depth, alpha Na, or TEPD but caused a slight increase in alpha K. Evaporation decreased depth; increased alpha Na, alpha K, and osmotic pressure; and changed TEPD. Measurements on preparations in vivo broadly supported these observations. In addition, the depth of ASL developed on isolated preparations was related to the humidity of the air to which animals had been previously exposed. We conclude that condensation and evaporation at the ASL-air interface in isolated preparations and in preparations in vivo do significantly modify key ASL variables as does the relative humidity of the air to which animals are exposed before experimentation.

Animals↗

PubMed1994

Regulation of airway surface liquid on the isolated guinea-pig trachea.

Isolated guinea-pig tracheae exposed to conditioned air mucosally and to circulating saline solutions serosally have been subjected to an osmotic gradient between saline and airway surface and to a range of drugs. Experiments were conducted to examine the mechanisms that regulate airway surface liquid during condensation and evaporation. Measurements were made of the depth of airway surface liquid, its sodium activity, the transepithelial potential difference, and of net water and sodium transport across the airway. Results suggest that osmotic gradients have profound effects on airway surface liquid but drugs that influence secretory activity (methacholine, substance P) or ion transport activity (amiloride, bumetanide, oubain) do not.

Amiloride↗

PubMed1994

Evaporation-induced changes in airway surface liquid on an isolated guinea pig trachea.

An isolated preparation of the guinea pig trachea was developed. The trachea was exposed serosally to Krebs-Henseleit solution and mucosally to tidal airflow, designed to mimic conditions in vivo. The preparation establishes stable layers of airway surface liquid (ASL). Typical depth, transepithelial potential differences, and sodium activity are 200 microns, -3 mV, and 125 mM, respectively (approximate sodium concn 170 mM). When exposed to air with a vapor pressure deficit (VPD), evaporation of water occurs from ASL, ASL depth decreases, and the concentration of sodium ions in ASL increases. The water content of air passing over the trachea also increases. This measurement is compared with measurements of the change in volume of ASL, based on depth changes, to yield estimates of net water transport (NWT). Measurements of changes in the sodium content of ASL allow for the calculation of net sodium transport by the trachea. Evaporation rate, changes in the volume of ASL, NWT, and net sodium transport are all influenced by VPD. The results suggest that evaporation from ASL increases its sodium concentration (and osmotic pressure) and increases osmotically driven NWT to replace water lost. Evaporation-induced increases in the sodium concentration appear to be limited by enhanced sodium uptake at high VPD.

Animals↗

PubMed1992

Studies on the fish gill microclimate.

An isolated and perfused fish gill filament preparation has been developed to facilitate investigations on the fish gill microclimate. Measurements have been made of the concentration of sodium at the lamellar surface and in the mixed-exit water, and of the maximum interlamellar velocity. When the external water has a sodium concentration of 0.10 mmol.l-1, water at the gill surface has a mean sodium concentration of 0.146 mmol.l-1. Mixed-exit water, 50 microns behind the perfused filament, has a mean sodium concentration of 0.118 mmol.l-1. When the water flowing over the filament has a maximum velocity of 18 cm.s-1, the maximum velocity between secondary lamellae is 1.5 cm.s-1. These measurements have been used to support the development of a velocity-modified diffusion model which describes ion movement in the interlamellar space. The analysis and observations on the preparation suggest that substantial unstirred layers do not exist at the lamellar surfaces in this preparation. Simple diffusion to and from the tissue surfaces, in conjunction with parabolic velocity profiles within the interlamellar spaces adequately explain net sodium movements.

Animals↗

PubMed1989

The effects of mucus and mucilaginous materials on ion-distributions at epithelial surfaces.

Mucous layers on epithelial surfaces may have a range of functions. One approach used to investigate these is to measure the distribution of ions within the mucous layers using ion-sensitive microelectrodes. The results of several studies are reviewed. It is clear that these layers do influence the distribution of ions at epithelial surfaces and by a variety of mechanisms. Processes such as active ion-transport and passive diffusion interact with the diffusional and ion-exchange properties of mucus to produce complex distributions.

Animals↗

PubMed1987

The influence of water pH on the perivitelline fluid of perch (Perca fluviatilis) eggs.

The diameter, trans-chorion potential difference and perivitelline-fluid pH of the eggs of perch (Perca fluviatilis) have been measured in a range of water pH (8-4.5). The water used was relatively nutrient rich. Eggs transferred from pH 8 to pH 4.5 shrink; probably as a result of loss of water from perivitelline fluid. Trans-chorion potential differences are close to zero over the range of pH. Mean perivitelline-fluid pH is higher than external water pH at pH 6.7 and above. Below pH 6.7, mean perivitelline-fluid pH is approximately the same as external water pH. The results suggest a non-Donnan distribution of hydrogen ions. The results are compared with data on salmonid eggs in nutrient-poor waters.

Acid-Base Equilibrium↗

PubMed1984

The influence of mucus on the diffusion of chloride ions across the oesophagus of the minnow (Phoxinus phoxinus L.).

Micro-electrodes sensitive to Cl- have been used to measure Cl- activities in the mucous layer on the mucosal surface of an isolated oesophageal preparation of the fresh-water teleost, Phoxinus phoxinus (L.). The technique has also been used to estimate the diffusion coefficient of Cl- in mucus in situ on the mucosal surface of this preparation. The mucous layer supports a linear gradient of Cl- which represents approximately 20% of the gradient of Cl- between mucosal and serosal solutions. The estimate of the diffusion coefficient of Cl- in mucus was 0.30 X 10(-5) +/- 0.029 X 10(-5) cm2 s-1 (mean +/- S.E. of mean, n = 13). This value is approximately 20% of published values of the diffusion coefficient in pure NaCl solutions or in teleost saline. It is suggested that the mucous layer acts to lower the permeability of the oesophagus in two ways. Its viscous and gel-forming nature encourages the formation of an unstirred layer, through which diffusion is the only means whereby salts can move. Also, it provides a layer through which Cl- and possibly other ions diffuse much more slowly than they would through a similar layer of mucosal solution without mucus.

Animals↗