ISSN:
1432-1424
Schlagwort(e):
Bicarbonate secretion
;
Cl−/HCO 3 − exchange
;
SITS
;
Stationary microperfusion
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Biologie
,
Chemie und Pharmazie
Notizen:
Abstract Secretion of bicarbonate has been described for distal nephron epithelium and attributed to apical Cl−/HCO 3 − exchange in beta-intercalated cells. We investigated the presence of this mechanism in cortical distal tubules by perfusing these segments with acid (pH 6) 10 mm phosphate Ringer. The kinetics of luminal alkalinization was studied in stationary microperfusion experiments by double-barreled pH (ion-exchange resin)/1 m KCl reference microelectrodes. Luminal alkalinization may be due to influx (into the lumen) of HCO 3 − or OH−, or efflux of H+. The magnitude of the Cl−/ HCO 3 − exchange component was measured by perfusing the lumen with solutions with or without chloride, which was substituted by gluconate. This component was not different from zero in control and alkalotic (chronic plus acute) Wistar rats. Homozygous Brattleboro rats (BRB), genetically devoid of antidiuretic hormone, were used since this hormone has been shown to stimulate H+ secretion, which could mask bicarbonate secretion. In these rats, no evidence for Cl−/HCO 3 − exchange was found in control BRB and in early distal segments of alkalotic animals, but in late distal tubule a significant component of 0.14±0.033 nmol/cm2 · sec was observed, which, however, is small when compared to the reabsorptive flow found in control Wistar rats, of 0.95±0.10 nmol/cm2 · sec. In addition, 5×10−4 m SITS had no effect on distal bicarbonate reabsorption in controls as well as on secretion in alkalotic Wistar and Brattleboro rats, which is compatible with the absence of effect of this drug on the apical Cl−/HCO 3 − exchange in other tissues. It is concluded that most distal alkalinization is not Cl− dependent, and that Cl−/HCO 3 − exchange may be found in cortical distal tubule, but its magnitude is, even in alkalosis, markedly smaller than the reabsorptive flux, which predominates in the rats studied in this paper, keeping luminal pH lower than that of blood.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF00233451
