| 19225053 |
Pergher PS, Leite-Dellova D, de Mello-Aires M: Direct action of aldosterone on bicarbonate reabsorption in in vivo cortical proximal tubule. Am J Physiol Renal Physiol. 2009 May;296(5):F1185-93. Epub 2009 Feb 18.
The direct action of aldosterone (10 (-12) M) on net bicarbonate reabsorption (J (HCO (3)(-))) was evaluated by stationary microperfusion of an in vivo middle proximal tubule (S2) of rat kidney, using H ion-sensitive microelectrodes. Aldosterone in luminally perfused tubules caused a significant increase in J (HCO (3)(-)) from a mean control value of 2.84 +/- 0.08 [49/19 (n degrees of measurements/n degrees of tubules)] to 4.20 +/- 0.15 nmol.cm (-2).s (-1) (58/10). Aldosterone perfused into peritubular capillaries also increased J (HCO (3)(-)), compared with basal levels during intact capillary perfusion with blood. In addition, in isolated perfused tubules aldosterone causes a transient increase of cytosolic free calcium ([Ca (2+)](i)), monitored fluorometrically. In the presence of ethanol (in similar concentration used to prepare the hormonal solution), spironolactone (10 (-6) M, a mineralocorticoid receptor antagonist), actinomycin D (10 (-6) M, an inhibitor of gene transcription), or cycloheximide (40 mM, an inhibitor of protein synthesis), the J (HCO (3)(-)) and the [Ca (2+)](i) were not different from the control value; these drugs also did not prevent the stimulatory effect of aldosterone on J (HCO (3)(-)) and on [Ca (2+)](i). However, in the presence of RU 486 alone [10 (-6) M, a classic glucocorticoid receptor (GR) antagonist], a significant decrease on J (HCO (3)(-)) and on [Ca (2+)](i) was observed; this antagonist also inhibited the stimulatory effect of aldosterone on J (HCO (3)(-)) and on [Ca (2+)](i). These studies indicate that luminal or peritubular aldosterone (10 (-12) M) has a direct nongenomic stimulatory effect on J (HCO (3)(-)) and on [Ca (2+)](i) in proximal tubule and that probably GR participates in this process. The data also indicate that endogenous aldosterone stimulates J (HCO (3)(-)) in middle proximal tubule. |
1(0,0,0,1) |