Determination of rheogenic ion transport in rat proximal colon in vivo

Abstract

A direct clamping technique is demonstrated, which allows monitoring of rapid changes of the short-circuit current (I _sc) and the specific transepithelial resistance (R _m) as well as measurement of ion fluxes under short-circuit conditions in vivo. Due to the cylindrical symmetry of the colon the intraluminal electrode was devised as a centrally fixed silver rod, by which radial current injection was achieved. The geometrical arrangement of the electrodes guaranteed zero potential difference (PD) along the whole axis of the colon segment. TheI _sc was determined to 3.3±0.7 μeq h⁻¹cm⁻² andR _m equal to 121±5 Ωcm². These data obtained by direct short-circuiting agree well with our earlierR _m andI _sc data based on cable analysis, where theI _sc was calculated from the open-circuit PD andR _m. This is considered as evidence for the reliability of the two independent in vivo techniques. Their validity was confirmed by the expected effects of drugs acting on rheogenic ion transport. Both the indirect (viaR _m) as well as the directI _sc determination may be used alternatively as required; one may serve to match the other. For larger tubular structures like the rat colon the direct clamping should be prefered as the standard procedure for theI _sc determination in vivo.