Abstract
The effective thickness of the unstirred fluid layer (USL) adjacent to an epithelial barrier can be estimated from the time course for the accumulation or depletion of a solute at the membrane surface. In 1985 we reported an unstirred layer thickness of approximately 70 microns for Necturus gallbladder epithelium. In our earlier studies the delay caused by noninstantaneous bulk solution mixing was not taken into account and thus the USL thickness was systematically overestimated. In the present studies we describe an analysis of the time course of solute arrival at the membrane surface that takes into account noninstantaneous bulk solution mixing. We also describe a simple technique to monitor the accumulation or depletion of a solute at the membrane surface. The time course for the change in the concentration of either tetramethylammonium (TMA+) or tetrabutylammonium (TBA+) upon elevation of bulk solution concentration is sensed at the membrane surface with an ion-sensitive microelectrode. Because of the high selectivity of the ion-sensitive resin for TMA+ or TBA+ over other monovalent cations in the solution (Na+ and K+), a low concentration (1- 2 mM) of the probe can be used. By measuring the time course of the arrival of first one probe and then the other, under identical superfusion conditions, sufficient information is obtained to eliminate multiple fits to the data, obtained when only one probe is used. Neglecting bulk solution mixing caused an error greater than 50% in estimated apparent USL thickness. The effective thickness of the USL depends critically upon chamber geometry, flow rate, and the position of superfusion and suction pipettes. Under our experimental conditions the effective USL at the mucosal surface of Necturus gallbladder epithelium was approximately 40 microns.
Full Text
The Full Text of this article is available as a PDF (911.2 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Andreoli T. E., Troutman S. L. An analysis of unstirred layers in series with "tight" and "porous" lipid bilayer membranes. J Gen Physiol. 1971 Apr;57(4):464–478. doi: 10.1085/jgp.57.4.464. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Barry P. H., Diamond J. M. Effects of unstirred layers on membrane phenomena. Physiol Rev. 1984 Jul;64(3):763–872. doi: 10.1152/physrev.1984.64.3.763. [DOI] [PubMed] [Google Scholar]
- Bindslev N., Tormey J. M., Wright E. M. The effects of electrical and osmotic gradients on lateral intercellular spaces and membrane conductance in a low resistance epithelium. J Membr Biol. 1974;19(4):357–380. doi: 10.1007/BF01869986. [DOI] [PubMed] [Google Scholar]
- Dainty J., House C. R. Unstirred layers in frog skin. J Physiol. 1966 Jan;182(1):66–78. doi: 10.1113/jphysiol.1966.sp007809. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Diamond J. M. A rapid method for determining voltage-concentration relations across membranes. J Physiol. 1966 Mar;183(1):83–100. doi: 10.1113/jphysiol.1966.sp007852. [DOI] [PMC free article] [PubMed] [Google Scholar]
- GINZBURG B. Z., KATCHALSKY A. THE FRICTIONAL COEFFICIENTS OF THE FLOWS OF NON-ELECTROLYTES THROUGH ARTIFICIAL MEMBRANES. J Gen Physiol. 1963 Nov;47:403–418. doi: 10.1085/jgp.47.2.403. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Green K., Otori T. Direct measurements of membrane unstirred layers. J Physiol. 1970 Mar;207(1):93–102. doi: 10.1113/jphysiol.1970.sp009050. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Marban E., Rink T. J., Tsien R. W., Tsien R. Y. Free calcium in heart muscle at rest and during contraction measured with Ca2+ -sensitive microelectrodes. Nature. 1980 Aug 28;286(5776):845–850. doi: 10.1038/286845a0. [DOI] [PubMed] [Google Scholar]
- Neher E., Lux H. D. Rapid changes of potassium concentration at the outer surface of exposed single neurons during membrane current flow. J Gen Physiol. 1973 Mar;61(3):385–399. doi: 10.1085/jgp.61.3.385. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Pedley T. J. Calculation of unstirred layer thickness in membrane transport experiments: a survey. Q Rev Biophys. 1983 May;16(2):115–150. doi: 10.1017/s0033583500005060. [DOI] [PubMed] [Google Scholar]
- Reuss L. Changes in cell volume measured with an electrophysiologic technique. Proc Natl Acad Sci U S A. 1985 Sep;82(17):6014–6018. doi: 10.1073/pnas.82.17.6014. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Strange K., Spring K. R. Methods for imaging renal tubule cells. Kidney Int. 1986 Aug;30(2):192–200. doi: 10.1038/ki.1986.171. [DOI] [PubMed] [Google Scholar]
- Westergaard H., Dietschy J. M. Delineation of the dimensions and permeability characteristics of the two major diffusion barriers to passive mucosal uptake in the rabbit intestine. J Clin Invest. 1974 Sep;54(3):718–732. doi: 10.1172/JCI107810. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Wilson F. A., Dietschy J. M. The intestinal unstirred layer: its surface area and effect on active transport kinetics. Biochim Biophys Acta. 1974 Aug 21;363(1):112–126. doi: 10.1016/0005-2736(74)90010-8. [DOI] [PubMed] [Google Scholar]