Scanning Microscopy


Cytoplasmic monovalent ion and water contents in morphologically defined mice jejuna) cells were measured by X-ray microanalysis in order to gain insight into the cell-type specificity of intestinal electrolyte transport mechanisms. Ion and water contents were measured independently. It was found that in some cases net fluxes of ions and water do not correspond to the assumption of constant osmotic activity of cytoplasmic Na and K ions. Stimulation of secretion with the cholinergic secretagogue pilocarpine resulted in efflux of Cl- from and influx of K+ into crypt enterocytes containing small secretion granula (crypt A cells). No significant changes in ion concentrations were found in crypt enterocytes without secretion granula (crypt B cells). Crypt A cells were more likely to be stimulated by pilocarpine than crypt B cells, and the basolateral K+ efflux pathway in crypt A cells appeared to be rate-limiting. In villus enterocytes, pilocarpine stimulated Cl- efflux. Isoproterenol caused marked changes in the cytoplasmic Cl content of all epithelial cells. These changes were reversed by inhibition of adenylate cyclase by alloxan, with the sole exception of Cl increase in villus absorptive cells. The results are consistent with an cAMP-mediated stimulated secretion in crypt epithelial cells and a predominantly cAMP-independent stimulation of absorption in villus cells. The results obtained suggest a transcellular route of Cl absorption in the mouse jejunum.

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