Models of electrolyte absorption and secretion by gastrointestinal epithelia

An attempt has been made to account for the electrolyte transport properties of several gastrointestinal epithelia in terms of relatively simple cell models. In doing so, it becomes apparent that the complex patterns of electrolyte absorption and secretion by tissues such as in vitro rabbit ileum may actually represent a combination or superposition of several basic transport processes that can be more readily identified in other epithelia. Thus, attempts to explain the effects of agents such as cyclic AMP in terms of a single mechanism of action may prove to be unproductive for such tissues. Clearly, our approach has involved certain speculations and, undoubtedly, oversimplifications. Only those processes which appear to be responsible for sodium and chloride transport have been dealt with in any detail; much remains to be learned about the processes responsible for the absorptive and secretory movements of other ions, principally HCO3. However, this analysis may be useful in bringing a degree of uniformity to a complex area and, hopefully, has identified certain important gaps in our understanding of electrolyte transport at the cellular level which require further investigation.