Search PubMed⌕ Search

Biomedical subjects

M M Civan

Publications and source records attributed to M M Civan.

At least 91 records · Page 5Linked to original sources
PubMed1980

Potassium activities in epithelia.

In general, intracellular K+ appears to be compartmentalized. This phenomenon does not seem to characterize cytoplasm per se, but probably reflects the processes of sequestration and ion exclusion characterizing certain as yet unidentified organelles. The cell nucleus does not appear to participate significantly in these processes. Measurement of intracellular potassium activity (alpha K)c in small epithelial cells is complicated by significant technical problems. Recent experimental maneuvers designed to circumvent these problems have led to substantially higher estimates of (alpha K)c under baseline conditions. The time courses of short circuit current (SCC) and (alpha K)c in toad urinary bladder have been correlated under two experimental conditions. After removing external K+ or after adding ouabain, both parameters are depressed. However, the time courses of SCC and (alpha K)c are very different following return to baseline conditions. The data suggest: 1) that the processes of cell K+ accumulation and transepithelial Na+ transport are not linked with a fixed stoichiometry, and 2) if a reduction in cytosolic K+ activity does inhibit transepithelial Na+ transport, its role is indirect.

Animals↗
PubMed1978

Activity coefficients of intracellular Na+ and K+ during development of frog oocytes.

The chemical activities, (a), of Na+ and K+ were determined in large mature and in small immature frog oocytes, using open-tipped micropripettes and ion-selective microelectrodes. The average chemical concentrations, c, of Na+ and K+ were determined by spectrophotometry and by electron probe X-ray microanalysis. The apparent activity coefficient (gammaapp) was calculated for each ion as the ratio, a/c. With development, (aNa/ak) decreased four to fivefold and (cNa/cK) increased six to sevenfold. In the large mature oocytes, gammaapp was measured to be 0.08 +/- 0.02 and gammaappK lay within the range 1.15 +/- 0.03 to 1.29 +/- 0.04, constituting the smallest value for Na+ and largest value for K+, respectively, thus far reported. This intracellular value of gammaappK was substantially greater than the activity coefficient of K+ in the external medium (0.76). The data suggest that the inequality of gammaappNa and gammaappK in this and probably other cells reflects the development of subcellular compartmentalization of ions. Possible intracellular sites of ionic compartmentalization are considered.

Animals↗
PubMed1978

Pathways for movement of ions and water across toad urinary bladder. III. Physiologic significance of the paracellular pathway.

Hypertonicity of the mucosal bathing medium increases the electrical conductance of toad urinary bladder by osmotic distension of the epithelial "tight" or limiting junctions. However, toad urine is not normally hypertonic to plasma. In this study, the transmural osmotic gradient was varied strictly within the physiologic range; initially hypotonic mucosal bathing media were made isotonic by addition of a variety of solutes. Mucosal NaCl increased tissue conductance substantially. This phenomenon could not have reflected soley an altered conductance of the transcellular active transport pathway since mucosal KCl also increased tissue conductance, whether or not Na+ was present in the bathing media. The effect of mucosal NaCl could not have been mediated solely by a parallel transepithelial pathway formed by damaged tissue since mucosal addition of certain nonelectrolytes also increased tissue conductance. Finally, the osmotically-induced increase in conductance could not have occurred soley in transcellular transepithelial channels in parallel with the active pathway for Na+, since the permeability to 22Na from serosa to mucosa (s to m) was also increased by mucosal addition of NaCl; a number of lines of evidence suggest that s-to-m movement of Na+ proceeds largely through paracellular transepithelial pathways. The results thus establish that the permeability of the limiting junctions is physiologically dependent on the magnitude of the transmural osmotic gradient. A major role is proposed for this mechanism, serving to conserve the body stores of NaCl from excessive urinary excretion.

Animals↗
PubMed1978

The relationship between the transverse and longitudinal nuclear magnetic resonance relaxation rates of muscle water.

Whole frog sartorius and gastrocnemius muscles were incubated in Ringer's solutions, either unenriched or enriched with H2 17Oor 2D2O. Subsequently, the rates of transverse (1/T2) and of longitudinal (1/T1) nuclear magnetic relaxation were measured for 17O, 2D, and 1H at room temperature and at 8.1 MHz. The ratio (T1/T2) for 17O was measured to be approximately 1.5-2.0, close to the value roughly estimated from the Larmor frequency dependence of 1/T1 alone over the range 4.3-8.1 MHz. On the other hand (T1/T2) for 2D and 1H were both measured to lie in the range 9-11. Insofar as the entire 17O signal was detected, the data indicate the presence of an exchange mechanism between the major fraction of intracellular water and a minor fraction characterized by enhanced rates of relaxation. Possible molecular mechanisms are presented.

Animals↗
PubMed1978

Intracellular activities of sodium and potassium.

The intracellular contents of Na+ and K+ appear to modulate a variety of cellular and tissue functions, including transepithelial transport. However these total ionic contents appear to consist of heterogeneous populations of Na+ and K+. No more than a few percent of intracellular Na+ and K+ appear bound. Thus, the heterogeneity of the intracellular ionic contents must reflect subcellular compartmentalization. Recent technical advances in the preparation and use of ion-selective microelectrodes have permitted progress in defining the possible sites of such intracellular compartmentalization. Furthermore, intracellular recording with microelectrodes and micropipettes now provides a technique with which to directly monitor the chemical activities of Na+ and K+ within the cytoplasm as a function of the state of transepithelial transport. This approach has already provided information necessitating a reexamination of certain classical concepts of transport physiology.

Animals↗
PubMed1977

Pulsed nuclear magnetic resonance study of 39K within halobacteria.

The 39K contents of isolated pellets and supernatant solutions from suspensions of Halobacterium halobium were studied at 21-22 degrees C by pulsed NMR spectroscopy. The rates of transverse relaxation were measured directly from the free induction decay (FID). The rate of longitudinal relaxation was measured by studying the FID after pairs of pulses of approximately 90 degrees. Care was exercised to minimize the effect of magnetic field inhomogeneity; its contribution to the FID was approximately 25-30 sec-1. The transverse relaxation process was found to consist of at least two components, whose rates were 321-449 sec-1 and 1,122-2,067 sec-1. In one preparation where the longitudinal relaxation process was studied, the data could be well fit to a single exponential relaxing at 253 +/- 33 (mean +/-95% confidence limits) sec-1. Comparison of the relative intensities of the NMR signals with the results of atomic absorption photometric analyses indicated that the great bulk of the intracellular 39K was detected by the NMR techniques used. The data obtained from the current NMR of H. halobium are consistent with: (1) fractional binding of less than 3% of the total intracellular K+, (2) a small ordering factor characterizing all of the intracellular K+, or (3) some combination of the two.

Computers↗
PubMed1976

Pulsed nuclear magnetic resonance study of 17O from H217O in rat lymphocytes.

Lymphocytes obtained from thymus glands of normal rats and culture lines of malignant rat thymocytes were enriched with H217O. The longitudinal and transverse relaxations of the 17O were determined separately in samples of packed cells and supernatant solutions. The longitudinal relaxation of intracellular 17O of fresh viable lymphocytes was nonexponential, becoming simply exponential with eventual necrosis. The rate of spin-lattice relaxation (1/T1) was fitted by a sum of two exponentials. The average mole fraction of the molecules subject to the slower relaxation rate (1/T1s) was two-thirds of the total water. Lowering the Larmor frequency (omega) from 7.72 to 4.36 MHZ increased the faster component (1/T1f) by 12% without altering (1/T1s). The value of the single exponential decay of the nonviable cells was not appreciably different from the initial rate of relaxation of the fresh cells. Similar results were obtained in studies of the transverse relaxation rates. The simplest interpretation is that two-thirds of the cell water is located within the nucelus and is characterized by a slower rate of relaxation than the one-third of the cell water in the cytoplasm because of the different macromolecular compositions of the two-subcellular compartments. The malignant lymphocytes were characterized by prolonged values for the slow and fast components of both the longitudinal and transverse relaxations of 17O.

Animals↗
PubMed1976

Pulsed nuclear magnetic resonance study of 39K in frog striated muscle.

Samples of 1 M KCl solution and 10 samples of intact frog striated muscle were studied at 4-7 degrees C and/or at 21-22 degrees C. Field inhomogeneity was minimized by using small sample volumes and by using a superconducting magnet designed specifically to provide highly homogeneous fields. In the present experiments, magnetic field inhomogeneity was measured to contribute less than 15% to the free induction decay observed for intracellular 39K. The signal-to-noise ratio of the measurements was enhanced by means of extensive time-averaging. The rates of nuclear relaxation for 39K in aqueous solution were 22 +/- 3 (mean +/- 95% confidence limits) s-1 at 4-7 degrees C and 15 +/- 2 s-1 at 21-22 degrees C. For intracellular 39K, (1/T2) was measured to be 327 +/- 22 s-1 and 229 +/- 10 s-1 at the lower and higher temperatures, respectively. The corresponding values for (1/T1) in the same muscle samples were 198 +/- 31 s-1 and 79 +/- 15 s-1 at 4-7 degrees C and at 21-22 degrees C, respectively. These results for 39K are similar to those previously obtained for intracellular 23Na. Since less than 1% of the intracellular 23Na has been estimated to be immobilized, fractional immobilization of intracellular 39K is also likely to be insubstantial.

Animals↗
PubMed1976

Aldosterone and insulin effects on driving force of Na+ pump in toad bladder.

Both aldosterone and insulin increase active Na+ transport across the urinary bladder of the toad. Recent data have provided further support to the concept that aldosterone acts primarily to increase Na+ entry from the mucosal medium into the transporting cells, whereas insulin acts to increase active Na+ extrusion into the serosal medium. To examine this concept further, the driving force (E(Na)) of the Na+ pump was measured, by the technique described by Yonath and Civan (48), before and after hormonal administration. Both hormones increased short-circuit current, but only insulin increased E(Na). The validity of the technique was further explored by imposing periods of hypoxia upon a series of experimental hemibladders; as expected, hypoxia reversibly decreased E(Na). The data indicate that insulin stimulates Na+ transport, in part by directly stimulating the Na+ pump. The results are also consistent with the concept that aldosterone stimulates net Na+ movement solely by enhancing Na+ entry into the transporting cells, but are subject to alternative interpretations.

Aldosterone↗
PubMed1975

Intracellular distribution of free potassium in Chironomus salivary glands.

Potassium activities have been measured in the nucleus and cytoplasm of Chironomus salivary gland cells, using potassium-selective electrodes. The data provide the first rigorous evidence that potassium is at electrochemical equilibrium across the nuclear membrane. In addition, no difference in potassium chemical activity was found between nucleus and cytoplasm.

Animals↗
PubMed1975

NMR study of -17-O from H2-17-O in human erythrocytes.

Human erythrocytes were incubated in a Ringer's solution enriched with 10--18 per cent H2-17-O. The longitudinal relaxation time (T1) of the -17-O was determined separately in samples of red cell suspensions, packed cells, and supernatant. The longitudinal relaxation of -17-O in erythrocyte suspensions was non-exponential, reflecting water exchange across the cell membranes as well as relaxation processes inside and outside the cell. The T1 of intracellular -17-O is 4--5 times shorter than in the supernatant, similar to the enhancement of proton relaxation by hemoglobin in erythrocytes and free solution at the frequency applied (8.13 MHz). This datum is consistent with tht thesis that hemoglovin modifies the NMR relaxation behavior of water inside cells and in free solution in the same way. The rate constant (kx) for water exchange was calculated to be 60 and 107 s- minus 1 at 25 and at 37 degrees C, respectively. The apparent activation energy for kx over the temperature range 23--37 degrees C was 8.7 plus or minus 1.0 kcal/mole.

Cell Membrane Permeability↗
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↗
PubMed1975

Pulsed nuclear magnetic resonance study of 17-O, 2-D, and 1-H of water in frog striated muscle.

Whole gastrocnemius muscles were incubated in Ringer's solution enriched with H2-17O; the paired contralateral gastrocnemius muscles were incubated in a similar solution enriched with deuterons, as well. Subsequently, the longitudinal relaxation times (T1) were measured 17-O, 2-D, and 1-H, both at 8.1 MHz and at 4.3 MHz. The results indicate that: (a) the absolute values of T1 characterizing the three nuclides are different in muscle and pure water. (b) the longitudinal relaxation rates of all three have an identical frequency dependence over the range studied, (c) the ratio (T1)2D/(T1)17ois the same in muscle water and pure water, while the ratio (T1)1H/(T1)17o is 2.1 times greater in pure water than it is in muscle water, and (d) 30-49 percent substitution of 2-D for 1-H has very little effect on the spin-lattice relaxation of tissue water protons. These data suggest that muscle water is in rapid exchange between a small fraction of immobilized molecules and a large fraction of free water. The results render unlikely the possibility that hypothetical ordering of muscle water significantly contributes to its longitudinal relaxation.

Animals↗