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The influence of buffer pH, glucose and sodium ion concentration on the acid microclimate in rat proximal jejunum in vitro

  • Transport Processes, Metabolism and Endocrinology; Kidney, Gastrointestinal Tract, and Exocrine Glands
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Abstract

Surface pH of rat proximal jejunum as measured in vitro by pH-electrode was found to be significantly more acid than bulk bathing media of neutral pH. Below a bulk pH value between pH 4 and 5, surface pH was isohydric with bulk pH but with increasing alkalinity of the bulk pH, surface pH remained consistently more acidic. The maintenance of a low surface pH was sensitive to external medium glucose concentration, particularly between 2 and 10 mM concentration. A Lineweaver-Burk plot of the glucose-dependent decrement in surface pH demonstrated an apparentK m of 2 mM. Anoxia caused a significant elevation in the measured surface pH at 10 mM glucose concentration. Surface pH was found to be sensitive to buffer sodium ion concentration in the jejunum, an effect which was less marked in the distal ileum.

The measured low pH at the mucosal surface of rat jejunum experimentally confirms the ‘acid-microclimate’ hypothesis for drug absorption as originally proposed by Schanker and colleagues. The existence of a low pH has important consequences for the intestinal absorption of dissociable compounds. The implication for the experimental verification of active transport of solutes capable of dissociation is discussed.

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Authors and Affiliations

  1. Chemistry Dept., University of Aston in Birmingham, Gosta Green, B4 7ET, Birmingham, UK

    F. H. Lei & J. A. Blair

  2. Institute of Physiology, The University of Glasgow, G12 8QQ, Glasgow, UK

    M. L. Lucas

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  1. M. L. Lucas
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  2. F. H. Lei
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  3. J. A. Blair
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Lucas, M.L., Lei, F.H. & Blair, J.A. The influence of buffer pH, glucose and sodium ion concentration on the acid microclimate in rat proximal jejunum in vitro. Pflugers Arch. 385, 137–142 (1980). https://doi.org/10.1007/BF00588693

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  • DOI: https://doi.org/10.1007/BF00588693

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