A new technique for measuring water transport across the seawater eel intestine.

A new technique was developed for measuring net water flux across the eel intestine in vitro. The new perfusion method was suitable for long duration experiments because of continuous oxygen supply to both the external and the perfusion medium. Net water flux was calculated directly from the difference between the rates of effluent and perfusate flow without measuring the concentration of marker substances. The calculated value of net flux appears to be reliable because: its direction is always from mucosa to serosa in both everted and non-everted intestine; ouabain diminishes it to zero; it is identical with the standard water flux obtained under zero perfusion; and it is identical with the value obtained by means of [14C]PEG following the previous perfusion method. The net water fluxes obtained by the new method were steadier than those obtained with the previous complicated perfusion method. In this new experimental system, the net water flux and the transepithelial potential difference (PD) decreased gradually with time, and were not restored by application of adrenergic agonists or cortisol. These parameters were stimulated by 5 mmol l-1 L-alanine, but not by D-glucose, L-valine or L-glycine, indicating a specific action of L-alanine.