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Biomedical subjects

M M Civan

Publications and source records attributed to M M Civan.

At least 109 records · Page 6Linked to original sources
PubMed1972

Nuclear magnetic resonance of sodium-23 linoleate-water. Basis for an alternative interpretation of sodium-23 spectra within cells.

The (23)Na spectrum from liquid crystals of sodium linoleate in water has been studied by nuclear magnetic resonance (NMR) techniques. The integrated intensity of the visible central spectral line was 34-39% of the intensity of a reference sample containing an equal quantity and concentration of (23)Na nuclei. Since satellite signals were clearly demonstrable, the effect reflected a nuclear quadrupolar interaction rather than a splitting of the (23)Na into two populations of bound and free nuclei. It is proposed that a similar quadrupolar effect may be the basis for the apparent binding of the (23)Na observed in biological systems.

Animals↗
PubMed1972

17 O nuclear magnetic resonance spectrum of H 2 17 O in frog striated muscle.

Whole striated muscles from the frog Rana esculenta were bathed in Ringer's solution enriched with H(2) (17)O; the muscle water was subsequently collected by vacuum distillation. The integrated intensity of the nuclear magnetic resonance (NMR) signal of (17)O in the muscle was measured to be approximately (3/4) of the signal observed in the distilled water. The phenomenon may arise either from immobilization of a population of the water molecules which may be a very small fraction or as much as (1/4) of the total, or may reflect tumbling of (1/3) of the water molecules in a compartment containing an anisotropic medium. Such an effect was demonstrated for H(2) (17)O using the model system of sodium linoleate in water.

Animals↗
PubMed1970

The effect of smooth muscle on the intercellular spaces in toad urinary bladder.

Phase microscopy of toad urinary bladder has demonstrated that vasopressin can cause an enlargement of the epithelial intercellular spaces under conditions of no net transfer of water or sodium. The suggestion that this phenomenon is linked to the hormone's action as a smooth muscle relaxant has been tested and verified with the use of other agents effecting smooth muscle: atropine and adenine compounds (relaxants), K(+) and acetylcholine (contractants). Furthermore, it was possible to reduce the size and number of intercellular spaces, relative to a control, while increasing the rate of osmotic water flow. A method for quantifying these results has been developed and shows that they are, indeed, significant. It is concluded, therefore, that the configuration of intercellular spaces is not a reliable index of water flow across this epithelium and that such a morphologic-physiologic relationship is tenuous in any epithelium supported by a submucosa rich in smooth muscle.

Acetylcholine↗
PubMed1969

Toad urinary bladder: intercellular spaces.

Vasopressin causes dilation of the intercellular spaces of the mucosal epithelium in toad bladder, an effect previously thought to result from enhanced net transepithelial water transport. Under conditions of zero net fluid transport, vasopressin exerted the same effect in seven tissues, which indicates that the width of the intercellular spaces cannot be taken as a reliable index of net transepithelial fluid transport.

Animals↗
PubMed1969

The anatomic site of the transepithelial permeability barriers of toad bladder.

An examination of the mucosal epithelium of the urinary bladder of the toad reveals that the two major cell types which abut on the urinary surface, the granular and mitochondria-rich cells, also contact the basement membrane. Thus, the epithelium functions as a single cell layer. Although basal cells are interpolated between the granular cells and the basement membrane over a large portion of the epithelium, they do not constitute an additional continuous cell layer. This finding is consistent with extensive physiological data which had assumed that the major permeability barriers of this epithelium were the apical and basal-lateral plasma membranes of a single layer of cells.

Animals↗
PubMed1968

The site of the stimulatory action of vasopressin on sodium transport in toad bladder.

Vasopressin increases the net transport of sodium across the isolated urinary bladder of the toad by increasing the mobility of sodium ion within the tissue. This change is reflected in a decreased DC resistance of the bladder; identification of the permeability barrier which is affected localizes the site of action of vasopressin on sodium transport. Cells of the epithelial layer were impaled from the mucosal side with glass micropipettes while current pulses were passed through the bladder. The resulting voltage deflections across the bladder and between the micropipette and mucosal reference solution were proportional to the resistance across the entire bladder and across the mucosal or apical permeability barrier, respectively. The position of the exploring micropipette was not changed and vasopressin was added to the serosal medium. In 10 successful impalements, the apical permeability barrier contributed 54% of the initial total transbladder resistance, but 98% of the total resistance change following vasopressin occurred at this site. This finding provides direct evidence that vasopressin acts to increase ionic mobility selectively across the apical permeability barrier of the transporting cells of the toad bladder.

Animals↗
PubMed1966

Contraction kinetics of striated muscle fibres following quick changes in load.

1. The contraction kinetics of single striated muscle fibres and small fibre bundles from the frog and the toad were measured when the load was changed from P(0) to L < P(0). Simultaneous recordings were made of displacement at one end and force at the other end of the preparation.2. After the load was changed, the contractile force generally reached a steady value before the contraction velocity became steady. The amount of time required for isotonic contraction to become steady depended on the change in fractional load and on the temperature; it did not depend on sarcomere length in the range 2.2-3.0 mu or on the number of fibres in the preparation. The characteristics of the non-steady state are described in terms of the displacement deviation (the difference between the actual displacement at a given time and the back extrapolation of the steady phase of the displacement record) and the null times (the times at which the displacement deviation became zero, measured relative to the time at which the contractile force first reached the value of the load).3. The time average of the transient velocity was approximately equal to the final steady velocity.4. The product of the null time following a given relative force step and V(max), the steady velocity of unloaded contraction, was found to be independent of temperature. This is taken as evidence that the isotonic velocity transients originate in the contractile mechanism.5. The non-steady state following step changes in load is identified with the motion of cyclic contraction mechanisms. The motion of the specific model formulated by A. F. Huxley (1957) was compared with that of frog muscle fibres and, although the transients in the two systems differ in detail, the characteristic dimensions are of the same order.

Animals↗