A mass spectrometer to measure transepithelial unidirectional labeled water fluxes

A sealed quartz micropipette forms a liquid-vacuum interface that together with a uranium reduction element and a mass spectrometer functions as an in vitro real-time labeled water-selective microelectrode. Its performance is demonstrated by monitoring unidirectional fluxes across toad urinary bladder. This instrument has direct applicability to studies of water flux across epithelial membranes and could also be useful in monitoring water fluxes across such preparations as isolated tubules or capillaries.