Mechanisms of H+/HCO3− Transport in Rat Kidney Medullary Thick Ascending Limb. Effects of Arginine Vasopressin

The thick ascending limb (TAL) of rat kidney absorbs bicarbonate and substantial rates (Good et al. 1984) that may account for much of the bicarbonate absorbed from Henle’s loop in vivo (about 15% of the bicarbonate filtered load, Bichara et al. 1984). Yet, the cellular mechanisms of H+/HCO3 − transport by the rat TAL have been studied in only a few studies that have reported in the cortical segment the presence of a luminal Na+:H+ antiport (Good 1985) and of a basolateral Na+: (HCO3 −)n>1 symport (Krapf 1988). Also, in the medullary segment (MTAL) of the mouse TAL, a luminal Na+:H+ antiport and a basolateral Na+:(HCO3 −) n >1 symport have been described (Kikeri et al. 1990).