Abstract
Certain changes occurring in gastrointestinal tissue as a result of irradiation of the animal seem to involve the active transport mechanisms concerned with secretion or absorption of electrolytes (1), and at lower doses these changes occur in the absence of gross disturbances in diffusional transfer fluxes (2). The present study employing bioelectric parameters arose in the attempt to study irradiation effects on these active transport mechanisms by a more general approach than that employing singleand double-label tracers. Although this aim is achieved at the expense of information on the specific source of bioelectric activity, the approach seemed desirable for several reasons: Ion flux measurements can be obtained by in vivo tracer techniques of tested validity, but flux values show an inherently high biological variability (2, 3), unlike potential measurements. Also, similar measurements in isolated rat stomach have been hampered by necessary experimental com-promises related to tissue thickness, which may render a tracer analysis by itself equivocal (4). A more serious problem with flux measurements is that the ions metabolically transported may differ. In frog stomach active chloride secretion is believed to account primarily for the observed bioelectric potential (5), but in rat colon active sodium absorption is believed to account primarily for the observed potential (6), and in rat ileum both active sodium and active chloride movements are reported (7). The existence of a gastric sodium pump has been demonstrated in fetal and term rabbits (8), and in this connection we recently reported the specificity and quantitative dependence of all gastric bioelectric parameters on sodium ion in adult rat stomach maintained in vitro (9, 10). Despite these differences, bioelectric parameters should monitor the relative rate at which ions metabolically pumped precede counter ions moving by other means. The potential would measure the summated effects
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