 Bumetanide

Bumetanide is an organic sulfonamide compound used as a loop diuretic. Its neutral molecular formula is ${\mathrm{C}}_{17}{\mathrm{H}}_{20}{\mathrm{N}}_2{\mathrm{O}}_5\mathrm{S}$. It inhibits salt transport through NKCC2, the renal sodium–potassium–chloride cotransporter, making it useful both pharmacologically and as an experimental probe of membrane transport.^[ref]

In a 1994 study, cloned kidney transporters were expressed in Xenopus laevis oocytes and distinguished by their transport behaviour and inhibitor sensitivity. This connected bumetanide-sensitive uptake to a specified transporter rather than to an unspecified effect of a crude tissue preparation.^[ref]

The usual NKCC2 transport cycle couples one sodium ion, one potassium ion and two chloride ions. Their transported charges sum to $+1+1-2=0$: a process can move substantial amounts of salt while remaining electrically neutral. An uptake measurement can therefore reveal inhibition even when net electric current alone would be an inadequate readout.