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D A Dick

Publications and source records attributed to D A Dick.

At least 37 records · Page 2Linked to original sources
PubMed1975

Sodium fluxes in single amphibian oocytes: further studies and a new model.

1. The kinetics of Na efflux were studied in oocytes of Bufo bufo, Rana temporaria and R. pipiens. 2. Rate constants for Na efflux into Ringer solution varied from 0-002 min-minus 1 to 0-017 min-minus 1 and did not vary significantly from one species to another. 3. Na efflux is rapidly reduced by 30-50% on removing external K or applying ouabain but is reduced by 90% on cooling to 0 degrees C. The effects of K and cooling are also rapidly reversible. 4. Substitution of external Na by Li produces a slow decline of Na efflux. Reversal on restoring external Na is, however, rapid even in the presence of ouabain. 5. When external Na is replaced by Li in the presence of ouabain, the normal decline in Na efflux does not occur. 6. When external Na has been replaced by Li, application of ouabain causes little or no further decline in Na efflux. 7. These results are interpreted quantitatively by means of a model which proposes that intracellular membrane-bounded channels (IMBC) contain 10-30% of the intracellular Na and provide a channel for its expulsion from the cell via connexions with the cell surface. It is supposed that Na is expelled actively from the cytoplasm into the IMBC as well as at the cell surface. Na expulsion via the IMBC is supposed to be insensitive to external K or ouabain. This model accounts for the results using parameters consistent with other investigations by autoradiography and Na-sensitive micro-electrodes. 8. Preliminary electron micrographic evidence shows channels which appear to lead from the cell surface into the cytoplasm and which may correspond with the proposed IMBC of the model.

Animals↗
PubMed1974

Intracellular sodium and potassium concentrations in toad and frog oocytes during development.

1. During growth of oocytes of Bufo bufo from approximately 700-2000 mum in diameter, intracellular Na rose from 20 to 120 m-mole/l. cell water while K fell from 120 to 15 m-mole/l. cell water.2. In Rana temporaria Na similarly rose from 9 to 190 m-mole/l. cell water and K fell from 126 to 28 m-mole/l. cell water.3. At the same time in both Bufo and Rana the ouabain-sensitive Na efflux, the ouabain-insensitive Na efflux, and the total Na influx all increased.4. It is concluded that the predominant process is an increase of passive Na permeability. The increase of apparently active Na efflux may be secondary to the consequent rise in intracellular Na.

Animals↗
PubMed1973

Location of inexchangeable sodium in the nucleus and cytoplasm of oocytes of Bufo bufo exposed to sodium-free solutions.

1. In oocytes exposed to Ringer solution in which Li substitutes for Na, 13-62% Na is inexchangeable with Li.2. Nuclei of oocytes isolated by dissection in salt solutions swell irrespective of the concentration or ionic components of the solution. When isolated in 4% bovine albumin solutions, swelling is negligible.3. When the nuclei of cells exposed to Li are isolated in 4% albumin solution, less than 6% of the inexchangeable Na is found in the nucleus, while 36-88% of it is found in the cytoplasmic fragments remaining after removal of the nucleus.4. When a Li-exposed cell is crushed in a cellophane bag and dialysed against Ringer or Li-substituted Ringer, 86-92% of the inexchangeable Na diffuses out.5. It thus appears that the inexchangeable Na is located almost entirely in the cytoplasm and hardly at all in the nucleus, and is not bound to macromolecules within the cell.

Albumins↗
PubMed1972

The red cell.

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Erythrocytes↗
PubMed1970

Autoradiographic demonstration of inhomogeneous distribution of sodium in single oocytes of Bufo bufo.

1. Autoradiography of frozen cells labelled with (22)Na has been used to locate a sequestered fraction of internal Na in the oocyte which exchanges very slowly or not at all with external Li.2. Relative grain density in nucleus and cytoplasm, measured photometrically, was used as an indication of (22)Na distribution within the oocyte. In test experiments grain density fell to 50% within 19 mum of the edge of the section. Owing to the large diameter of the oocyte (> 600 mum) and its nucleus (> 200 mum), this resolution was adequate to determine cytoplasmic/nuclear (C/N) ratios of grain density.3. In oocytes fully loaded with (22)Na, the mean C/N ratio was 0.92 +/- 0.03 (n = 11). After 5 hr exchange in Li-substituted Na-free Ringer solution, the mean C/N ratio was 2.18 +/- 0.04 (n = 11). After 5 hr exchange in Ringer solution as a control, the mean C/N ratio was 1.39 +/- 0.18 (n = 7). The cytoplasm thus contained a fraction of (22)Na inexchangeable with Li, and more slowly exchangeable with Na than that in the nucleus.4. The non-Li-exchangeable fraction of internal Na thus revealed appeared to be quantitatively similar to that already demonstrated by studies of (22)Na fluxes and of internal Na activity by means of Na-sensitive micro-electrodes.

Animals↗
PubMed1969

Inhibition of adenosine triphosphatase in sheep red cell membranes by oxidized glutathione.

This paper reports inhibition of Na(+) + K(+)-stimulated, ouabain-inhibited adenosine triphosphatase (S-ATPase) in sheep red cell membranes by oxidized glutathione (GSSG). The results are consistent with the hypothesis that this inhibition depends upon the formation of a mixed disulfide between glutathione and -SH group(s) in the enzyme protein. Thus, inhibition of S-ATPase by GSSG proceeds more rapidly at alkaline than at neutral pH and is reversed by the addition of an excess of a compound containing reduced -SH groups (e.g. dithiothreitol). ATP protects S-ATPase against inhibition by GSSG and this protection depends on both the monovalent and divalent cation composition of the medium. Protection by ATP is more complete in the presence of K(+) than in the presence of Na(+).

Adenosine Triphosphatases↗
PubMed1969

The activities and concentrations of sodium and potassium in toad oocytes.

1. The activity of potassium, a(K), in the cytoplasm of oocytes from the toad, Bufo bufo, as measured by potassium-sensitive glass micro-electrodes, was 82 mM. The concentration of potassium, C(K), in oocytes from the same ovaries, as determined by flame photometric analysis, was 113 mM. The ratio a(K)/C(K) = 0.73 does not differ significantly from the measured activity coefficient of the normal Ringer bathing solution, which is 0.75.2. The activity of sodium, a(Na), in the cytoplasm of toad oocytes, as measured by sodium-sensitive glass micro-electrodes, was 9.3 mM. The concentration of sodium, C(Na), in oocytes from the same ovaries, as determined by flame photometric analysis, was 25.8 mM. The value of the a(Na)/C(Na) ratio in the cells, 0.36, is only about half the value of either the a(K)/C(K) ratio in the cells or the activity coefficient of sodium in the normal Ringer bathing solution. This implies that about half the sodium in the cell is sequestered in some manner, such that it is unavailable to affect a cation-sensitive micro-electrode.3. When the oocytes were bathed for 5 hr in a sodium-free, lithium-substituted, Ringer solution the a(Na)/C(Na) ratio decreased to 0.06-0.10. This drop in the a(Na)/C(Na) ratio implies that the sodium available to the cation-sensitive micro-electrode can leave the cell much faster than the sequestered sodium.

Animals↗