Characteristics of Hydrogen Ion Transport in Urinary Bladder of Water Turtle*

Self Cite

A B S T R A C T The function of carbonic anhvdrase in H+ secretion by the turtle bladder was studied in vitro. Dose response curves were obtained for the carbonic anhydrase inhibitors, acetazolamide and ethoxzolamide, with and without addition of C02 to the system. In addition, carbonic anhydrase was assayed in hoilogenates of mucosal cells. The activity in the homogenates was 155±16 U/g dry wt, of which only 11 U represented contamination from erythrocytes; after addition of 5 X 10-M acetazolamide, no enzyme activity was detectable.In the intact preparation free of exogenous C02, the dose response curve for acetazolamide showed two plateaus of inhibition, one at 50% and one at more than 80% inhibition. At 50% inhibition (from 5 X 10-to 5 X 10-M acetazolamide), H+ secretion was restored or enhanced by C02 addition to the same extent as bladders not exposed to acetazolamide. At concentrations of more than 1 X 10-4 M, H+ secretion was no longer restorable by C02. Unlike acetazolamide, ethoxzolamide caused progressive inhibition of H+ secretion in the C02-free system. The maximal extent of inhibition with ethoxzolamide and the behavior of inhibition in the presence of 2.5% C02 were the same as for acetazolamide. Evidence is presented that all surface epithelial cells secrete H+ and generate OH-within the cell interior. The capacity of cells to dispose of OH-by C02 hydroxylation varies with the availability of cytoplasmic carbonic anhvdrase. A small population of cells contains abundant carbonic anhydrase and secretes at high rates even when C02 is in short supply.On the basis of these results and histochemical data on the distribution of carbonic anhydrase within the mucosa, an analysis is presented of the epithelial organization of acidification by the turtle bladder.

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Carbonic Anhydrase Function and the Epithelial Organization of H+ Secretion in Turtle Urinary Bladder

Schwartz¹,

Rosen²,

Steinmetz³

1972

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“…Although these studies were concerned primarily with an examination of coupling between H+ secretion and transport of Na+ or Cl-, it proved useful to identify the ionic flows that contributed to the short-circuit current (SCC). The ions to be considered are the following: (a) Na+, which is transported actively from the mucosal (M) to serosal (S) medium (3,4), (b) Cl-, which is transported actively from M to S under some experimental conditions (5), and (c) H+, which is transported actively into M (2).…”

Section: Methodsmentioning

confidence: 99%

Independence of Hydrogen Ion Secretion and Transport of Other Electrolytes in Turtle Bladder*

Steinmetz¹,

Omachi²,

Frazier³

1967

Self Cite

Abstract. The relationship between hydrogen ion secretion and the transport of other electrloytes was examined in the isolated urinary bladder of the water turtle. Symmetrical solutions which were free from exogenous carbon dioxide and bicarbonate bathed the two surfaces of the preparation, and the spontaneous electrical potential of the bladder was nullified by a voltage clamp. Active transport of sodium from mucosal to serosal medium was confirmed by simultaneous bidirectional flux measurements and found to be slightly, but not significantly, greater than the short-circuit current. In the absence of sodium in the bathing solutions, the normal potential difference across the bladder reversed and the current required to nullify this reversed potential difference had the same magnitude as the simultaneously measured rate of hydrogen ion secretion. The results indicate that, under these experimental conditions, the bladder transports sodium and hydrogen ion actively, but that chloride movement does not contribute to the short-circuit current.The rate of secretion of hydrogen ion was not affected by replacement of the sodium in the bathing media by cesium, or by inhibition of sodium transport by dinitrophenol. Acidification continued when chloride in the solutions was replaced by sulfate, or when potassium or calcium was removed from the solution bathing the mucosal surface. Secretion of hydrogen ion by the turtle bladder is not dependent on the simultaneous transport of other electrolytes across the bladder.

“…Previous studies (1,2) have shown that in the absence of exogenous C02 and HCOi-the isolated bladder of the water turtle acidifies the solution, bathing its urinary surface by the secretion of hydrogen ion. The addition of HCOs-to the (S)1 side of the bladder reduces the net rate of acid secretion by a mechanism of HCOs-transport from the S to the urinary compartment (3).…”

Section: Introductionmentioning

confidence: 99%

“…To measure the rate of alkali entrance into M after the addition of HCOi-to S, the pH stat method was employed (1). Since measurement of the S to M HCOi-flux requires the absence of net H+ secretion, the M solution for each bladder was acidified to the pH at which net-acid secretion was zero (pH range 4.5-52), while the pH of S was adjusted with NaOH to 8.5 in the absence of exogenous C02 and HCOs (4 The production of lactate by the bladders was not measured in the present study in which the deoxygenation periods were short.…”

Section: Introductionmentioning

confidence: 99%

Energy dependence of urinary bicarbonate secretion in turtle bladder.

Oliver¹,

Himmelstein²,

Steinmetz³

1975

A B S T R A C T Addition of HCOi-to the serosal side (S) of the isolated turtle bladder results in a HCO0-flow from S to the mucosal side (M) which markedly reduces the net rate of acid secretion. To characterize the driving forces for this downhill HCO3-flow, the effects of metabolic inhibitors and substrates were examined. In short-circuited bladders with the M pH lowered to the point of zero net H+ secretion, the rate of HCO-entry into M in response to a 20-mM HCO3-gradient was measured by pH stat titration. Deoxygenation reduced the HC03-flux from 1.24±0.1 gM/h/8 cm2 (SEM) to 0.50±0.1 tM/h with glucose (2 X 10' M) and from 1.32±0.1 to 0.47±0.1 iAM/h without glucose.A similar reduction (61%) was observed in the presence of 1% C02. Dinitrophenol (10' M), cyanide (10' M), and deoxyglucose (10-' M) inhibited the HCO3-flux by 39%, 37%, and 38%, respectively. The combination of any of these inhibitors with N2 caused the same inhibition as Ns alone. In bladders depleted of substrate, pyruvate (5 X 10-' M) increased the HCOs-flux from 0.36 ±0.05 to 0.58±0.01 ,M/h (P < 0.005); the increment was abolished by deoxygenation.The results indicate that the bulk of the downhill HCOi-flow in this system is dependent on metabolic energy derived primarily from oxidative sources, and that this energy-dependent flow approximates the electroneutral component of HCO3-secretion that is coupled to Cl-absorption.