Summary
Proton secretion in the urinary bladder of the freshwater turtle is mediated by proton pumps located in the apical membrane of carbonic-anhydrase (CA)-rich cells. It has been proposed that the rate of proton transport is regulated by endocytotic and exocytotic fusion processes which alter the apical membrane area, and hence number of exposed pumps. Three techniques were used to study this process. Analyses of transepithelial impedance provided estimates of transport-associated changes in net membrane area, as well as other electrical parameters. Electron microscopy allowed visualization of the endocytotic vesicles thought to be involved in the process. Finally, uptake of a florescent fluid-phase markerprovided measurements of the rates of endocytosis. We report the following: (i) endocytotic and exocytotic processes occur primarily in the CA-rich cells; (ii) inhibition of proton transport resulting from 0.5mm acetazolamide (AZ) results in a decrease in the apical membrane area of approximately 0.47 cm2/cm2 tissue; (iii) the apical membrane specific conductance of the CA-rich cells is approximately 220 μS/μF, and possibly represents a Cl− conductance that may function in counter-ion flow; (iv) the decline in transport following AZ is not directly proportional to the decline in apical membrane area, suggesting that changes in pump kinetics are also involved in the regulation of transport; (v) the CA-rich cells exhibit a high rate of constitutive pinocytosis, and hence membrane shuttling, which appears to be independent of the rate of transport; (vi) AZ induces a transient increase in the rates of endocytosis and shuttling; and (vii) the transport-associated changes in apical membrane area may reflect an effect of AZ on a regulated endocytotic pathway which is distinct from the pinocytotic process.
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Cannon, C., Adelsberg, J. van, Kelly, S., Al-Awqati, Q. 1985. CO2-induced exocytotic insertion of H+ pumps in turtle-bladder luminal membrane. Role of cell pH and calcium.Nature (London) 314:443–446
Clausen, C., Dixon, T.E. 1986. Membrane electrical parameters in turtle bladder measured using impedance-analysis techniques.J. Membrane Biol. 92:9–19
Clausen, C., Fernandez, J.M. 1981. A low-cost method for rapid transfer function measurements with direct application to biological impedance analysis.Pfluegers Arch.390:290–295
Clausen, C., Reinach, P.S., Marcus, D.C. 1986. Membrane transport parameters in frog corneal epithelium measured using impedance analysis techniques.J. Membrane Biol. 91:213–225
Cole, K.S. 1972. Membranes Ions and Impulses. p. 12. University of California Press, Berkeley, California
Dixon, T.E., Al-Awqati, Q. 1979 Urinary acidification is due to a reversible proton translocating ATPase.Proc. Natl. Acad. Sci. USA 76:3135–3138
Dixon, T.E., Al-Awqati, Q. 1980. H+/ATP stoichiometry of proton pump of turtle urinary bladder.J. Biol. Chem. 255:3237–3239
Fischer, J.L., Husted, R.F., Steinmetz, P.R. 1983. Chloride dependence of the HCO3 exit step in urinary acidification by the turtle bladder.Am. J. Physiol. 245:F564-F568
Gluck, S., Cannon, C., Al-Awqati, Q. 1982. Exocytosis regulates urinary acidification in turtle bladder by rapid insertion of H+ pumps into the luminal membrane.Proc. Natl. Acad. Sci. USA 79:4327–4331
Gluck, S., Kelly, S., Al-Awqati, Q. 1982. The proton transporting ATPase responsible for urinary acidification.J. Biol. Chem. 257:9230–9233
Graber, M.L., Dixon, T.E., Coachman, D., Herring, K., Ruenes, A., Gardener, T., Pastoriza, E. 1986. Fluorescence identifies an alkaline cell in turtle urinary bladder.Am. J. Physiol. 250:F159-F168
Husted, R.F., Mueller, A., Kessel, R., Steinmetz, P.R. 1981. Surface characteristics of carbonic anhydrase rich cells in turtle urinary bladder.Kidney Int. 19:491–502
Lewis, S.A., Eaton, D.C., Clausen, C., Diamond, J.M. 1977. Nystatin as a probe for investigating the electrical properties of a tight epithelium.J. Gen. Physiol. 70:427–440
Maren, T.H. 1956. Carbonic anhydrase inhibition V. N5-substituted 2-acetylamino-1,3,4-thiadiazole-5-sulfonamides. Metabolic conversion and use as control substances.J. Pharmacol. Exp. Ther. 117:385–393
Masur, S.K., Cooper, S., Rubin, M.S. 1984. Effect of an osmotic gradient on antidiuretic hormone-induced endocytosis and hydrosmosis in the toad urinary bladder.Am. J. Physiol. 247:F370-F379
Parson, C.L., Mulholland, S. 1978. Bladder surface mucin.Am. J. Pathol. 93:423–432
Reeves, W., Gluck, S., Al-Awqati, Q. 1983. Role of endocytosis in H+ secretion.Kidney Int. 23:237
Rosen, S. 1972. Localization of carbonic anhydrase activity in turtle and toad urinary bladder mucosa.J. Histochem. Cytochem. 20:696–702
Satake, N., Durham, J.H., Ehrenspeck, G., Brodsky, W.A. 1983. An electrogenic mechanism for alkali and acid transport in turtle bladders.Am. J. Physiol. 244:C259-C269
Schultz, S.G. 1980. Basic Principles of Membrane Transport. Cambridge University Press, Cambridge
Schwartz, J.H. 1976. H+ current responses to CO2 and carbonic anhydrase inhibition in turtle urinary bladder.Am. J. Physiol. 231:565–572
Schwartz, J.H., Bethencourt, D., Rosen, S. 1982. Specialized function of the carbonic-anhydrase-rich and granular cells of turtle bladder.Am. J. Physiol. 242:F627-F633
Schwartz, J.H., Rosen, S., Steinmetz, P.R. 1972. Carbonic anhydrase function and the epithelial organization of H+ secretion in turtle urinary bladder.J. Clin. Invest. 51:2653–2662
Schwartz, J.H., Tripolone, M. 1983. Intracellular pH of granular and mitochondria rich cells of turtle bladder.Kidney Int. 23:239
Steinman, R.M., Mellman, I.S., Muller, W.A., Cohn, Z.A. 1983. Endocytosis and the recycling of plasma membrane.J. Cell. Biol. 96:1–27
Steinmetz, P.R. 1974. Cellular mechanisms of urinary acidification.Physiol. Rev. 54:890–956
Stetson, D.L., Steinmetz, P.R. 1983. Role of membrane fusion in CO2 stimulation of proton secretion by turtle bladder.Am. J. Physiol. 245:C113-C120
Stetson, D.L., Steinmetz, P.R. 1985. α and β types of carbonic anhydrase-rich cells in turtle bladder.Am. J. Physiol. 249:F553-F565
Weibel, E.R. 1979. Stereological Methods. Vol. 1. Practical Methods for Biological Morphometry. Academic, London
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Dixon, T.E., Clausen, C., Coachman, D. et al. Proton transport and membrane shuttling in turtle bladder epithelium. J. Membrain Biol. 94, 233–243 (1986). https://doi.org/10.1007/BF01869719
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DOI: https://doi.org/10.1007/BF01869719