Mortimer M. Civan

The cellular specificity of the effect of vasopressin on toad urinary bladder.

SummaryPhase and electron micrographs of toad bladders were obtained following dilution of bathing media in the presence and absence of vasopressin. Dilution of the mucosal medium alone resulted in no morphologic changes. Subsequent addition of vasopressin produced an increase in the cell volume of the granular cells, manifested by some or all of the following changes: increased area of granular cell profiles as observed in sections, rounding of the cell nucleus, displacement of the two components of the nuclear envelope, loss of nuclear heterochromatin, sacculation of the endoplasmic reticulum and the Golgi apparatus, and reduction in the electron density of the cell cytoplasm. No such morphologic changes were noted in the other cell types comprising the mucosal epithelium — the mitochondria-rich, the goblet, and the basal cells. On the other hand, dilution of the serosal bathing medium in the absence of vasopressin caused a marked increase in the cell volume of all these cell types. The results demonstrate that the action of vasopressin to enhance bulk water flow across toad bladder is exerted specifically on the apical surface of the granular cells. It is suggested that the hormonal effect on sodium transport may also be limited to the granular cells. The route of osmotic water flow and the possible role of the other mucosal epithelial cells is discussed.

Determination of the driving force of the Na+ pump in toad bladder by means of vasopressin

SummaryVasopressin stimulates Na+ transport across toad bladder largely or entirely by decreasing the resistance to Na+ entry into the transporting epithelial cells. Therefore, the hormone should induce proportional changes in short circuit current (IS) and tissue conductance; the ratio of these changes should equal the driving force (ENa) of the Na+ pump.Administration of vasopressin provided a rapid, reversible and reproducible technique for the measurement ofENa. Values calculated forENa ranged from 74 to 186 mV, in agreement with previously published estimates. The results were not dependent on the vasopressin concentration over a wide range of concentrations.Ouabain, an agent thought to inhibit specifically the Na+ pump, decreased bothIS andENa. On the other hand, amiloride, a diuretic thought to block specifically Na+ entry, markedly reducedIS, without reducingENa.It is concluded that vasopressin constitutes a probe for the rapid reproducible determination ofENa under a wide variety of physiological conditions.

Effects of vasopressin on the water and ionic composition of toad bladder epithelial cells

SummaryIsolated sheets of epithelial cells as well as epithelial cells scraped from paired hemibladders mounted in chambers both showed significant increases in water, sodium and chloride contents after exposure to vasopressin (100 mU/ml), without any change in potassium content. In the isolated cells these changes were prevented by amiloride (10−5m), suggesting that the gain of sodium after vasopressin occurs across the mucosal membrane. This hypothesis was confirmed in experiments in which it was found that, in hemibladders mounted in chambers and bathed on their mucosal surface by sodium Ringers with24Na, the gains of chemical sodium and24Na after vasopressin were equivalent.

Measurement of the composition of epithelial cells from the toad urinary bladder.

SummaryTwo methods are described by which epithelial cells from toad urinary bladders can be obtained for analysis of their intracellular water and electrolyte contents. In the first, a method similar to that described in 1968 by J. T. Gatzy and W. O. Berndt, sheets of epithelial cells are scraped from bladders after incubation in sodium Ringers and collagenase (400 mg/liter). The scraped cells were incubated under various conditions and their composition subsequently determined. Oxygen consumption was also measured. In the second method, epithelial cells were scraped from hemibladders removed from chambers. These cells were then analyzed without further incubation. The morphology of epithelial cells obtained by each method is illustrated. Both methods yield similar results and evidence is provided that the derived intracellular values obtained truly reflect the composition of the epithelial cells.

Clarification of the intercellular space phenomenon in toad urinary bladder.

SummaryVasopressin has been noted to increase the size of the intercellular spaces of toad bladder epithelium even in the absence of an osmotic gradient. The present studies demonstrate that the same phenomenon may be obtained in the presence or absence of a transepithelial gradient of glutaraldehyde indicating that the effect is not a fixation artifact. Morphologic evidence is presented demonstrating continuity between the epithelium and underlying smooth muscle. The data support the concept that not only net water flow, but also changes in smooth muscle tone can appreciably affect the epithelial geometry.

Path of bulk water movement through the urinary bladder of the toad

Vasopressin increases bulk water flow across the toad bladder. To resolve whether this flow proceeds primarily between or through the surface epithelial cells, the maximum intercellular flow rate was calculated. Since the experimental flow rate is 28 times the calculated maximum, bulk water flow is likely to proceed largely through the cells of the mucosal epithelium.

The effect of propionate and other organic anions on sodium transport across toad bladder.

Abstract 1. 1. The electrical effects of isotonic, isohydric solutions of propionate and other organic anions were studied in paired quarter-bladders obtained from the toad, Bufo marinus. 2. 2. Serosal propionate solutions produced large, reversible increases in transepithelial potential and short-circuit current, associated with a decrease in electrical resistance. These pH-dependent propionate effects persisted for several hours, and were greatest at concentrations of 66–88 mM. Serosal acetate, butyrate and pyruvate elicited similar responses, but of lesser magnitude. 3. 3. Isotonic concentrations of mucosal propionate slightly reduced the transepithelial potential and short-circuit current. 4. 4. Cationic substitution, 24Na+ flux, and O2-requirement studies demonstrated that the increased short-circuit current induced by serosal propionate was caused by an acceleration of O2-dependent Na+ transport from the mucosal to the serosal medium. 5. 5. The electrical effects of serosal propionate and vasopressin were independent.