Cyclic adenosine monophosphate-stimulated bicarbonate secretion in rabbit cortical collecting tubules.

The distribution of Na'-independent Cl --HCO3 exchange was studied in individual intercalated cells from in vitro perfused rabbit outer CCDs using dual excitation laser scanning confocal microscopy by measuring the pH1 response to sequential removal of Cl-from both sides of the tubule. Three patterns of intracellular pH (pH1) response were observed. 39% of intercalated cells had only apical Cl--HCO3 exchange (,B cell), 4%had only basolateral Cl--HCO-exchange (a cell), and 57% had both apical and basolateral Cl --HCO3 exchange (ay cell). Valinomycin-high K+ voltage clamping had no effect on the pH1 response of intercalated cells with bilateral Cl --HCO3 exchange. Although the mean rates of dpH1/dt following apical Cl-removal were similar in ,8 cells compared to y cells, a wide range ofapical rates was seen among individual iB and y intercalated cells. Neither the apical nor the basolateral CI--HCO3 exchanger in y cells was inhibited by 0.5 mM H2DIDS. Binding ofapical peanut lectin was seen both in ft cells and in y cells.In 41% of CCDs with four to seven intercalated cells studied, all intercalated cells were of the same subtype. We conclude that the majority of intercalated cells from the rabbit outer CCD have both apical and basolateral Na'-independent Cl--HCO3 exchangers (y cells), which are stilbene-insensitive. Intercalated cells with only basolateral CI--HCO3 exchange are very uncommon in the rabbit outer CCD. There is a tendency for all intercalated cells in a given rabbit outer CCD to be of the same subtype (either all 6 cells or all y cells), suggesting the presence of CCD intertubule heterogeneity at the same cortical level. This finding may account for intertubule differences in transepithelial H+-base transport. (J. Clin. Invest. 1994. 93:417423.)

Section: Methodssupporting

confidence: 75%

Functional characterization of three intercalated cell subtypes in the rabbit outer cortical collecting duct.

Emmons¹,

Kurtz²

1994

“…McKinney and Burg (5) first demonstrated HCO5 transport in the CCT and documented that chronic in vivo metabolic alkalosis stimulates net HCO5 secretion whereas chronic in vivo metabolic acidosis stimulates net HCO-absorption. Both of these processes are very similar to HCO-transport mechanisms in the turtle bladder (8)(9)(10)(11)(34)(35)(36).…”

Section: Discussionmentioning

confidence: 71%

“…Isolated perfused tubule studies demonstrate that the direction of net HCO transport by the CCT is influenced by the preexisting acid-base status of the animal from which the tubule was harvested (4,5,7). Tubules harvested from animals with chronic metabolic acidosis demonstrate augmented HCO absorption (4,5,7,8), whereas tubules harvested from animals with chronic metabolic alkalosis display enhanced HCO secretion (4,5,9,10). Thus, transport of HCO by the CCT can be influenced by chronic in vivo metabolic acid-base disturbances and furthermore appears to display a memory of the in vivo environment after being transferred to an in vitro system.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Regulation of net bicarbonate transport in rabbit cortical collecting tubule by peritubular pH, carbon dioxide tension, and bicarbonate concentration.

Breyer¹,

Kokko²,

Jacobson³

1986

The effects of changes in peritubular pH, carbon dioxide tension (Pco2), and HCO3 concentration on net HCO3 transport was examined in in vitro perfused cortical collecting tubules (CCTs) from unpretreated New Zealand white rabbits. Lowering peritubular HCO3 concentration and pH by reciprocal replacement of HCO3 with Cl-, significantly stimulated net HCO3 absorption. Lowering peritubular HCO3 concentration and pH, by substitution of HCO3 with gluconate, while keeping Cl-concentration constant, also stimulated net HCO3 absorption. Raising peritubular HCO3 concentration and pH, by reciprocal replacement of Cl-with HCO3, inhibited net HCO3 absorption (or stimulated net HCO3 secretion). When the tubule was cooled, raising peritubular HCO3 concentration had no effect on net HCO3 transport, suggesting these results are not due to the passive flux of HCO3 down its concentration gradient.The effect of changes in ambient Pco2 on net HCO3 transport were also studied. Increasing the ambient Pco2 from 40 mmHg to either 80 or 120 mmHg, allowing pH to fall, had no effect on net HCO3 transport. Similarly, lowering ambient Pco2 to 14 mmHg had no effect on net HCO3 transport. Simultaneously increasing peritubular HCO3 concentration and Pco2, without accompanying changes in peritubular pH, i.e., isohydric changes, stimulated net HCO3 secretion to the same degree as nonisohydric increases in peritubular HCO3 concentration. Likewise, isohydric lowering of peritubular HCO3 concentration and Pco2 stimulated net HCO3 absorption.We conclude that: (a) acute changes in peritubular HCO3 concentration regulate acidification in the CCI and these effects are mediated by a transcellular process; (b) acute changes in ambient Pco2 within the physiologic range have no effect on HCO3 transport in the in vitro perfused CCI; and (c) acute in vitro regulation of CCI acidification is independent of peritubular pH.

“…These studies identify the presence of an electroneutral Na+ -independent C1-/ HCO3-exchanger (7,8) which functions as a counterpoint to the acid extruding systems (NaI/H' exchanger and Na'-HCO-symport) (6) and which has been detected recently in the hepatocyte apical domain of human liver (9). The Cl-/ HCO3-exchanger is present in all the bicarbonate-secreting epithelia (10)(11)(12)(13)(14)(15)(16)(17)(18)(19). In biliary epithelium for example, this exchanger, functionally coupled with apically located C1-channels, is stimulated by secretin, a hormone which induces a ductular bicarbonate-rich choleresis (18,19).…”

Section: Introductionmentioning

confidence: 99%

Effect of glucagon on intracellular pH regulation in isolated rat hepatocyte couplets.

Alvaro¹,

Guardia²,

Bini³

et al. 1995

To elucidate mechanisms of glucagon-induced bicarbonaterich choleresis, we investigated the effect of glucagon on ion transport processes involved in the regulation of intracellular pH (pH1) in isolated rat hepatocyte couplets. It was found that glucagon (200 nM), without influencing resting pH1, significantly stimulates the Cl-/HCO3 exchange activity.The effect of glucagon was associated with a sevenfold increase in cAMP levels in rat hepatocytes. The activity of the Cl-/HCO3-exchanger was also stimulated by DBcAMP + forskolin. The effect of glucagon on the Cl-/HCO3 exchange was individually blocked by two specific and selective inhibitors of protein kinase A, uM) and H-89 (30 ,uM), the latter having no influence on the glucagon-induced cAMP accumulation in isolated rat hepatocytes. The Cl -channel blocker, NPPB (10 pmM), showed no effect on either the basal or the glucagon-stimulated Cl-/ HCO3 exchange. In contrast, the protein kinase C agonist, PMA (10 jpM), completely blocked the glucagon stimulation of the C1-/HCO3 exchange; however, this effect was achieved through a significant inhibition of the glucagonstimulated cAMP accumulation in rat hepatocytes. Colchicine pretreatment inhibited the basal as well as the glucagon-stimulated Cl-/HCO3 exchange activity. The Na+/H+ exchanger was unaffected by glucagon either at basal pH1 or at acid pH, values. In contrast, glucagon, at basal pH1, stimulated the Na+-HCO-symport. The main findings of this study indicate that glucagon, through the cAMP-dependent protein kinase A pathway, stimulates the activity of the Cl-/HCO3 exchanger in isolated rat hepatocyte couplets, a mechanism which could account for the in vivo induced bicarbonate-rich choleresis. (J. Clin. Invest. 1995.