Figure 9. Summary figure of dietary effects on furosemide actions on urinary K excretion.

A. On CTRL diet, furosemide blocks NKCC2, inhibiting net K⁺ reabsorption in the TAL while increasing distal Na⁺ delivery and flow, which stimulates K⁺ secretion through ROMK and BK in ASDN. The net effect of furosemide is an increase in urinary K⁺ excretion. B. On LNaHK diet, up-regulated NKCC2 and ROMK, possibly by Ang II, results in net K⁺ secretion in the TAL. Elevated aldosterone (Aldo) from LNaHK upregulates ENaC, ROMK, and BK in the ASDN to promote distal K⁺ secretion. Furosemide blocks NKCC2, inhibiting net K⁺ secretion in the TAL. Although furosemide increases distal Na⁺ delivery and flow that stimulate K⁺ secretion in ASDN, the net result is a decrease in urinary K⁺ excretion. Transporters in the basolateral membrane and cell types of ASDN have been omitted for simplicity.