Intra- and extracellular gradients of electrical potential and ion activities of the epithelial cells of the rabbit ileum in vivo recorded by microelectrodes

Abstract

The epithelial cells of the rabbit ileum are about 40 µm long and have a diameter of roughly 5 µm. They are closely packed in a columnar fashion with their mucosal ends facing the lumen of the intestine and their serosal ends abutting the basement membrane and facing the underlying capillaries, lymphatics and connective tissue. The inner wall of the intestine is coated with a layer of mucopolysacharides, the mucus layer. When Krebs solution or similar solutions are placed in the lumen it is well known (e.g. the review by Edmonds 1970) that the solution is transported into the underlying tissues. During this transport the sodium activity in the gut lumen remains constant, the chloride activity decreases and the bicarbonate activity increases. However, the relationship of the intra- to the extracellular environment of each individual cell during this transport is only little understood. In recent years the methods applied in the study of the state of the cells during this transport have mostly been of a type that requires preparation of the tissue in vitro , e.g. usage of flamephotometry and Ussing-chambers. In case of the intestine of warm-blooded animals such a choice of experimental conditions is unfortunate for several reasons: ( a ) The transport is no longer into the blood or lymphatic drainage, ( b ) the epithelial cells have to be oxygenated from their luminal ends which in vivo are normally at a very low oxygen concentration (Crompton, Silver & Shrimpton 1965) and ( c ) in some experiments the physiological parameters of the tissue change during the experiment (e.g. Powell, Binder & Curran 1973). However, the use of microelectrodes allows an in vivo approach since the tissue can be left in its natural environment during the measurements. Furthermore liquid ion exchanges and ion-sensitive glasses developed over the past few years have led to the construction of microelectrodes selective to various ions (Hinke 1959; Thomas 1970; Walker 1971), so that the state of cells in terms of intra- and extracellular electrical potential and ion activities can be determined. Thus intracellular sodium and potassium has been recorded in the epithelial cells of the bullfrog small intestine in vitro (Lee & Armstrong 1972). The purpose of this work was first to construct an in vivo model in which the epithelial cell layer of the rabbit ileum could be studied by microelectrodes and secondly to determine the intra and extracellular electrical potential and ion activities in these cells when the lumen of the intestine was filled with various salt solutions.