Relationship between sodium and bicarbonate transport in the rat proximal convoluted tubule

Abstract

The relationship between net sodium and bicarbonate transport was studied by microperfusion of proximal convoluted tubules and peritubular capillaries. Bicarbonate absorption was unchanged as long as the sodium concentration remained above 40 meq/liter, despite reduction of sodium transport to 10% of its control value. At a sodium concentration of 5 meq/liter, fluid absorption was completely abolished but bicarbonate transport was reduced to 39% of its control value. Even at reduction of luminal and peritubular sodium concentrations to nominally zero, bicarbonate transport continued at 23% of its control value. Amiloride, at a sodium concentration of 5 meq/liter, inhibited bicarbonate absorption in a dose-dependent manner. Elevating peritubular pH to 8.4 drastically reduced net bicarbonate transport, whereas fluid absorption was only slightly inhibited. These results are consistent with a dual mechanism of acidification: a sodium-hydrogen exchange that saturates at low extracellular sodium concentrations and an additional sodium-independent mechanism of hydrogen ion secretion.

Regulation of ammonia production by mouse proximal tubules perfused in vitro. Effect of luminal perfusion.

“…To ascertain whether flow-induced changes in ammonia production depended upon the flow-induced changes in the rate of fluid reabsorption observed in the proximal tubule (17), we perfused proximal segments with perfusate containing 25 mM sodium (sodium chloride isoosmotically replaced by mannitol) and 1.0 mM amiloride hydrochloride, a condition that has been shown to reduce fluid reabsorption in the rat proximal tubule (18). We found that fluid reabsorption by the mouse proximal tubule fell to -0.11±0.36 nl/mm per minute (n = 3) from a control value 1.09±0.26 nl/mm per minute.…”

Effect of luminal and peritubular HCO3(-) concentrations and PCO2 on HCO3(-) reabsorption in rabbit proximal convoluted tubules perfused in vitro.

“…First, Giebisch et al (33) found that H+ secretion was reduced when NaHCO3 was infused acutely to obtain a plasma HCO-concentration of 44 mM. Second, Chan and Giebisch (34) observed that increasing peritubular HCO-concentration from 2 to 40 mM inhibited HCO-reabsorption. However, the interpretation of these data as indicating an independent effect of peritubular HCO-concentration is complicated by the presence of extracellular volume expansion in the former and by the presence of an extremely low peritubular Pco2, and thus high pH, in the latter.…”

The Role of Na+−H+ Exchange in Fluid and Solute Transport in the Rat Efferent Ducts

“…There are conflicting reports concerning the extent to which luminal fluid may be acidified between the seminiferous tubules and the caput epididymidis (Levine & Kelly, 1978;Caflisch & DuBose, 1990). It is well documented that proximal tubule fluid is acidified by H¤ secretion (see review in Alpern & Rector, 1996;also Lucci et al 1980;DuBose et al 1981) and there is evidence that the Na¤-H¤ antiporter contributes largely to this (Chan & Giebisch, 1981;Howlin et al 1985;Preisig et al 1987). The apical Na¤-H¤ exchanger has also been implicated in epididymal acidification (Au & Wong, 1980).…”