Renal bicarbonate reabsorption in the rat. I. Effects of hypokalemia and carbonic anhydrase.

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Bicarbonate transport was studied in vivo by separate microperfusion experiments of early and late distal tubules. Total CO2 was measured by microcalorimetry and fluid absorption by 3H-inulin. Significant bicarbonate absorption was observed in all experimental conditions. Bicarbonate transport was loaddependent upon increasing the luminal bicarbonate concentration from 15 to 50 mM in both early and late distal tubule segments and remained constant at higher concentrations at a maximum rate of 100-110 pmol/min per mm. At low lumen bicarbonate concentrations (15 mM), higher rates of bicarbonate absorption were observed in early (32.9±4.57 pmol/min per mm) as compared to late distal tubules (10.7±3.1 pmol/ min per mm). Amiloride and ethyl-isopropylamiloride both inhibited early but not late distal tubule bicarbonate absorption whereas acetazolamide blocked bicarbonate transport in both tubule segments. Fluid absorption was significantly reduced in both tubule segments by amiloride but only in early distal tubules by ethyl-isopropylamiloride. Substitution of lumen chloride by gluconate increased bicarbonate absorption in late but not in early distal tubules. Bafilomycin Al, an inhibitor of HATPase, inhibited late and also early distal tubule bicarbonate absorption, the latter at higher concentration. After 8 d on a low K diet, bicarbonate absorption increased significantly in both early and late distal tubules. Schering compound 28080, a potent H-K ATPase inhibitor, completely blocked this increment of bicarbonate absorption in late but not in early distal tubule. The data suggest bicarbonate absorption via Na+-H+ exchange and H-ATPase in early, but only by amiloride-insensitive H' secretion (H-ATPase) in late distal tubules. The study also provides evidence for activation of K+-H+ exchange in late distal tubules of K depleted rats. Indirect evidence implies a component of chloride-dependent bicarbonate secretion in late distal tubules and suggests that net bicarbonate transport at this site results from bidirectional bicarbonate movement. (J. Clin.

Section: Methodssupporting

confidence: 93%

“…The method used to measure total CO2 has been described previously and was carefully followed (4,7). Collected The solutions used in this study are given in Table I.…”

Section: Methodsmentioning

confidence: 99%

Renal bicarbonate reabsorption in the rat. IV. Bicarbonate transport mechanisms in the early and late distal tubule.

Wang¹,

Malnic²,

Giebisch³

et al. 1993

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“…These cells also contain abundant carbonic anhydrase activity (39, 40). Under appropriate conditions, the distal convoluted tubule of the rat has substantial rates of H+ secretion (43). Our results suggest that a proton pump may contribute to H+ transport or to intracellular pH regulation in this segment, but a role for Na+/H+ exchange or other acid/ base transporters has not been excluded.…”

Section: Immunocytochemistrymentioning

confidence: 69%

Localization of a proton-pumping ATPase in rat kidney.

Brown¹,

Hirsch²,

Gluck³

1988

319

192

The distribution of vacuolar H'ATPase in rat kidney was examined by immunocytochemistry using affinity-purified antibodies against the 31-, 56-, and 70-kD subunits of the bovine kidney proton pump. Proximal convoluted tubules were labeled over apical plasma membrane invaginations, and in the initial part of the thin descending limb, apical and basolateral plasma membranes were moderately stained. Thick ascending limbs and distal convoluted tubules were apically stained although the intensity was greater in the distal convoluted tubule. Collecting duct principal cells were virtually unlabeled, but intercalated cells had intense staining with an apical, basolateral or diffuse pattern in the cortex, and exclusively apical staining in the medulla. These results (a) show the presence of an H'ATPase in the apical plasma membrane of the proximal tubule that may contribute to H+ transport in this segment; (b) provide direct evidence that the intercalated cell contains most of the H'ATPase detectable in the collecting duct, supporting its proposed role in H+ transport; (c) demonstrate that subpopulations of cortical intercalated cells have opposite polarities of an H'ATPase, consistent with the presence of both proton-and bicarbonate-secreting cells; and (d) suggest a role for the H+ATPase in acid/base regulation or H+ transport in segments other than the collecting duct and the proximal tubule.

“…Bicarbonate reabsorption along the cortical distal tubule ofthe rat kidney has been studied by both in vivo micropuncture and microperfusion techniques (1)(2)(3)(4)(5). Owing to technical difficulties in isolating these segments, studies in isolated perfused mammalian distal tubules have been scarce (5), and no data are available on bicarbonate reabsorption and acidification.…”

Section: Introductionmentioning

confidence: 99%

Renal bicarbonate reabsorption in the rat. III. Distal tubule perfusion study of load dependence and bicarbonate permeability.

Chan¹,

Malnic²,

Giebisch³

1989

Self Cite

Using continuous microperfusion techniques, we studied the load dependence of bicarbonate reabsorption along cortical distal tubules of the rat kidney and their bicarbonate permeability. Net bicarbonate transport was evaluated from changes in tracer inulin concentrations and total CO2 measurements by microcalorimetry. Bicarbonate permeability was estimated from the flux of total CO2 along known electrochemical gradients into bicarbonate-and chloride-free perfusion solution containing l0'-M acetazolamide.