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Biomedical subjects

A D Macknight

Publications and source records attributed to A D Macknight.

At least 55 records · Page 3Linked to original sources
PubMed1976

Relationships between serosal medium potassium concentration and sodium transport in toad urinary bladder. II. Effects of different medium potassium concentrations on epithelial cell composition.

Epithelial cells from hemibladders incubated in potassium-free sodium Ringer's serosal medium lost potassium, both in exchange for serosal sodium and with chloride and water. Cellular sodium of mucosal origin did not change. The loss of cellular potassium, chloride and water closely followed the fall in short-circuit current (SCC). One third as much potassium, chloride and water were lost in 1 mM potassium serosal medium; SCC fell 1/3 as much. Potassium-free choline Ringer's serosal medium abolished the initial increase in SCC and reduced the fall in cellular potassiu, chloride and water and in SCC. Ouabain (10(-2)M) in potassium-free medium prevented the initial increase in SCC and the loss of cellular chloride and water. Ouabain (5 X 10(-4)M) caused loss of cellular potassium in exchange for mucosal and serosal sodium, effects different from those of absence of serosal potassium although SCC was similarly inhibited. Sodium-free mucosal medium abolished SCC and prevented the initial transient of SCC and diminished loss of cellular potassium, chloride and water on removing serosal potassium. When serosal potassium concentration was increased considerably, cells gained potassium, chloride and water, and in 116 mM potassium media, lost sodium of serosal origin. A hypothesis is advanced to explain the transients in SCC on changing serosal potassium concentration. The fall in cellular potassium, not water, probably inhibits sodium transport in media of less than 2 mM potassium.

Animals↗
PubMed1976

Relationships between serosal medium potassium concentration and sodium transport in toad urinary bladder. III. Exchangeability of epithelial cellular potassium.

The exchangeability of toad bladder epithelial cell potassium has been investigated. An insignificant amount of cellular potassium exchanged with mucosal medium 42K. From the rate of uptake of 42K into the cells from the serosal medium at least two cellular potassium pools were identified. The more rapidly exchanging pool contained about one-quarter to one-third of the cellular potassium and exchanged with a half-time of about 30 min. It was from this pool that potassium was lost from cells exposed to ouabain or to a potassium-free medium. In addition, when 3.5 mM rubidium replaced 3.5 mM potassium in sodium Ringer's the epithelial cells lost in 60 min about one-quarter of their cellular potassium in exchange for rubidium. Inhibition of transepithelial sodium transport by amiloride, 10(-5) mM, seemed to depress the rate of potassium uptake into the more rapidly exchanging pool without affecting total cellular potassium content. However, stimulation of transepithelial sodium transport by vasopressin appeared not to affect the rate of potassium uptake. The rate of potassium uptake into this pool seemed much less than that required for a tight 1:1 coupling between transepithelial sodium transport and potassium uptake. The remaining cellular potassium exchanged at a much slower rate and even after 19 hours of incubation only 67% of cellular potassium was labelled. If this slower exchanging potassium represents a single pool, 99% of cellular potassium would be labelled only after incubation with 42K for 56 hours.

Animals↗
PubMed1975

The sodium transport pool in toad urinary bladder epithelial cells.

The sodium which equilibrates with 24-Na in epithelial cells of toad urinary bladders has been determined. With sodium Ringer's bathing both mucosal and serosal surfaces, 24-Na in the mucosal medium equilibrated with about 35 mmoles cellular sodium/kg cellular dry weight, representing about 20% of the total cellular sodium determined flame photometrically; 24-Na in the serosal medium equilibrated with 120 mmoles cellular sodium/kg cellular dry weight, about 80% of the total cellular sodium. With 24-Na in both media all cellular sodium was labeled within 30 min. In the absence of serosal sodium, total cellular sodium and that sodium which equilibrated with mucosal 24-Na in sodium Ringer's were both similar to the cellular sodium of mucosal origin which had been determined in epithelial cells exposed on both surfaces to sodium Ringer's. Sodium-free mucosal medium, and sodium Ringer's containing amiloride 10-4 or 10-3 M in the mucosal medium, both virtually completely inhibited transepithelial sodium transport. But, whereas the cellular sodium of mucosal origin fell to only 2 mmoles/kg cellular dry weight with sodium-free mucosal medium, an appreciable labeling of cellular sodium was found whether amiloride was present before, or only after, exposure of tissue to mucosal 24-Na. Rapid washing of the mucosal surface of hemibladders just before removal of epithelial cells for analysis removed most of this sodium labeled in the presence of amiloride, suggesting that the cellular sodium of mucosal origin consists of at least two fractions with only about two-thirds truly intracellular. The sodium transport pool measured directly in these experiments is appreciably smaller than any previous estimates of pool size all of which have been obtained by indirect techniques involving use of whole hemibladders rather than epithelial cells alone.

Amiloride↗
PubMed1975

Some effects of ouabain on cellular ions and water in epithelial cells of toad urinary bladder.

Transepithelial sodium transport was virtually abolished when toad urinary hemibladders, mounted in chambers and short-circuited, were exposed on their serosal surface to ouabain, 10-2 M,for 60 minutes. Epithelial cells scraped from such hemibladders gained sodium and lost an equal quantity of potassium when compared with controls not exposed to cardiac glycoside. Their total cellular cation content, chloride content and water content were unchanged. Experiments in which 24-Na, amiloride, or sodium-free mucosal solutions were used, revealed that a large, though variable, percentage of the sodium gained by cells exposed to oubain, came from the mucosal medium, a finding consistent with the model of passive sodium entry from the mucosal medium followed by active sodium extrusion to the serosa. The oubain-insensitive maintenance of cellular volume which was observed did not depend upon transepithelial sodium transport which had been virtually completely inhibited by ouabain. Neither did the maintenance of a normal cellular potassium content depend upon transepithelial sodium transport, for cellular potassium was unaffected when the mucosal medium was sodium-free or when it contained sufficient amiloride, 10-3 M, to virtually abolish such transport.

Amiloride↗
PubMed1974

The regulation of cellular volume in liver slices.

1. Rat, rabbit and guinea-pig liver slices were incubated in media at 37 degrees C to study effects of ouabain and of metabolic inhibition on tissue composition.2. Slices initially incubated in oxygenated balanced medium did not swell when exposed to either balanced media or potassium-free media containing ouabain in concentrations ranging from 0.1 to 10 mM though they lost potassium and gained a comparable amount of sodium.3. Without prior incubation in oxygenated medium slices initially swelled when incubated with ouabain but then maintained their new volume.4. Slices whose metabolism was inhibited by incubation with nitrogen and 1 or 10 mM iodoacetamide lost as much potassium as slices exposed to 10 mM ouabain but became swollen with the uptake of sodium, chloride and water.5. The results show that liver cells, like renal cortical cells, possess a metabolically dependent, ouabain-insensitive, potassium-independent mechanism concerned in the regulation of cellular volume.

Acetamides↗
PubMed1974

Extracellular space in some isolated tissues.

1. The spaces occupied by isotopically labelled inulin, polyethylene glycol, mol. wt. 4000 (PEG 4000), polyethylene glycol, mol. wt. 1000 (PEG 1000) and sucrose in metabolizing mammalian kidney and liver slices and in toad bladder epithelial cell preparations incubated in vitro have been examined.2. In slices of mammalian tissue, and in homogenized liver, it proved impossible to extract inulin completely from tissue which had been dried. However, inulin was recovered as completely from both dried and undried toad bladder epithelial cells scraped from hemibladders incubated in vitro.3. PEG 4000 occupied a space in all preparations similar to that from which inulin was extracted in dried tissue.4. PEG 1000 and sucrose entered cellular water in mammalian slices, but PEG 1000 occupied a similar space to inulin in toad bladder epithelial cell preparations.6. It is concluded that inulin enters cellular water in mammalian slices from which after drying of the slices it cannot be extracted. It thus rather fortuitously provides a measure of extracellular water under these conditions. In preparations of toad bladder epithelial cells inulin seems to be a satisfactory extracellular marker. PEG 4000, which did not appear to enter cellular water also allows a reasonable estimate of extracellular water. PEG 1000 is a suitable extracellular marker for toad bladder epithelial cell preparations but not for mammalian slices. Sucrose entered cellular water in both slices and toad bladder epithelial cells and is not a satisfactory extracellular marker in these tissues.

Age Factors↗
PubMedDate not supplied

Formation of the aqueous humor.

1. Glaucoma is a worldwide disease affecting approximately 1-2% of the population aged over 35 years in industrial countries and is a major cause of blindness. 2. Glaucoma is usually associated with an increased intraocular pressure reflecting an imbalance between the rate of production of fluid (the aqueous humor) by the ciliary epithelial cells and its drainage from the eye. Therefore, it is important to understand how this secretion is produced. This requires a knowledge of ciliary epithelial cell composition, which has, in the past, proved difficult to obtain in mammalian preparations. 3. We have recently used the technique of electron-probe X-ray microanalysis to determine this composition under a variety of in vitro conditions. 4. Our results have led to a new model for this secretion that emphasizes the potential secretory role of the Na+/K+/2Cl- cotransporter.

Animals↗
PubMedDate not supplied

Principles of cell volume regulation.

Cell volume is determined by the content of osmotically active solute (cell osmoles) and the osmolarity of the extracellular fluid. Cell osmoles consist of non-diffusible and diffusible solutes. A large fraction of the diffusible cation content balances negative charges on the non-diffusible solutes. The content of diffusible solutes is determined by the electrochemical gradients driving them across the plasma membrane and the availability and activity of transport pathways in the membrane. The classical view that the sodium pump offsets passive leaks must be modified to accommodate the contributions of a number of secondary active transport processes, as well as to allow for changes in cell nondiffusible osmoles and in their net negative charge. The behaviour of cells in anisosmotic media is often different from that predicted for a perfect osmometer. In many cases this is a consequence of changes in cell osmole content. However, caution is required in extrapolating from in vitro responses of isolated cells to large, acutely induced changes in medium osmolality to the responses of tissues in vivo to more subtle changes in extracellular osmolality.

Animals↗
PubMedDate not supplied

Effects of impermeant medium ions on the composition of rabbit renal cortical slices.

When incubated in isosmotic oxygenated medium in which chloride was completely replaced by gluconate, rabbit renal cortical slices lost chloride with sodium, potassium and water before reaching a new steady-state composition after 15-30 min. When corrected for extracellular space, there was an electroneutral loss of alkali metal cations (Na + K) with chloride, accompanied by isosmotic loss of water from the cells. The losses of chloride and water were independent of medium pH over the range of 6.4-8.2, and were the same with potassium rather than sodium as the dominant medium cation. Incubation in isosmotic sodium chloride medium restored tissue composition of slices transferred from gluconate medium. This recovery was not dependent specifically upon medium chloride, for slice water content also recovered when nitrate rather than chloride was substituted for medium gluconate. With sodium completely replaced by n-methyl d-glucamine (nmdG+), cells in slices lost far more sodium and potassium than chloride before reaching a new steady-state composition after some 30 min. However, the loss of water was as predicted from the total losses of measured inorganic ions. With sodium and chloride completely replaced by nmdG+ and gluconate, there was a greater loss of water than found with unilateral substitutions. Again, the combined loss of diffusible inorganic cations exceeded the loss of chloride but the water loss was that expected for isosmotic loss accompanying the measured losses of ions. These results reveal that both gluconate and nmdG+ behave as impermeant ions in this tissue preparation. It is suggested that, in the absence of medium sodium, sodium-hydrogen exchange is inhibited. Retained hydrogen ions are buffered on charged cellular non-diffusible solutes and the associated hydroxyl (or bicarbonate) ions are lost from the cells accompanied by the inorganic univalent cations lost in excess of chloride in nmdG+ medium.

Animals↗