title: Luminal flow rate regulates proximal tubule H-HCO3 transporters.
abstract: In vivo microperfusion was used to examine the mechanism of luminal flow rate dependence of proximal tubule acidification. Luminal flow rate was acutely changed between 5 and 40 nl/min, while luminal and peritubular capillary composition were held constant. With inhibition of basolateral membrane base transport by peritubular 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), cell pH (pHi) provides a sensitive index of apical membrane H secretory activity. At a luminal perfusate [HCO3] of 25 mM, progressive increases in luminal flow rate (5----15----25----40 nl/min) caused progressive increases in pHi. This effect was of a smaller magnitude with a luminal perfusate [HCO3] of 60 mM and was further decreased at a luminal perfusate [HCO3] of 100 mM. This pattern of diminished flow rate dependence at higher luminal [HCO3] is consistent with the presence of a luminal unstirred layer, whose composition can be modified by luminal flow rate. The activity of the apical membrane Na-H antiporter, assayed as the initial rate of pHi recovery from an acid load in the presence of peritubular DIDS, was faster at 40 compared with 5 nl/min. Basolateral membrane Na-3HCO3 symporter activity, assayed as the initial rate of pHi recovery from an alkali load in the absence of luminal and peritubular chloride, was faster at 40 compared with 5 nl/min. This effect was eliminated by luminal amiloride, suggesting an indirect effect of flow mediated by changes in pHi secondary to flow rate-dependent changes in apical membrane Na-H antiporter activity. In summary, increases in luminal flow rate directly increase apical membrane H secretion, possibly by modification of a luminal unstirred layer.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas 75235-8856.
authors.forename: P A
authors.initials: PA
authors.lastname: Preisig
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000378:metabolism* / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D010477:Perfusion; D051381:Rats; D011919:Rats, Inbred Strains; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers
chemical_list: D001639:Bicarbonates; D002352:Carrier Proteins; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers