Adaptation of rabbit cortical collecting duct to in vitro acid incubation
Yasoshima, K.; Satlin, L.M.; Schwartz, G.J.
American Journal of Physiology 263(4 Pt 2): F749-F756
1992
ISSN/ISBN: 0002-9513 PMID: 1415745 Document Number: 403890
Cortical collecting ducts (CCDs) isolated from acid-loaded rabbits and perfused in vitro absorbed HCO-3-, whereas CCDs from normal animals secrete HCO-3-. We have previously shown that CCDs incubated in vitro for 3 h at pH 6.9 show a reduction in net (baseline and stimulated) HCO-3- secretion. In this study we ascertained the minimum duration of an acidic stimulus necessary to induce adaptive changes in stimulated HCO-3- (determined in the absence of basolateral Cl-) and the roles of protein synthesis and cytoskeletal function in this process. CCDs incubated in acid (pH 6.8, HCO-3- 6 mM) for 1 h followed by incubation at pH 7.4 (HCO-3- 25 mM) for 2 h showed a 41% reduction in stimulated HCO-3- secreted (P lt 0.001), similar to that observed after 3 h of incubation at pH 6.8. However, this incubation protocol failed to enhance stimulated HCO-3- absorption (determined in the absence of luminal Cl-). Addition of 10 mu-M anisomycin, a reversible inhibitor of protein synthesis, throughout the entire period of incubation (1 h at pH 6.8 plus 2 h at pH 7.4) blocked adaptive reduction in HCO-3- secretion, as did exposure to anisomycin only during the initial 1 h of acid incubation. In contrast, anisomycin application during the 2-h incubation at pH 7.4 failed to block this adaptation of HCO-3- secretion. Application of 4 mu-M actinomycin D, an inhibitor of DNA transcription, during the acid incubation also prevented the adaptive response, as did application during the total or during the 2-h pH 7.4 incubation period of 0.2 mu-M cytochalasin D, an inhibitor of actin filament function. Thus, HCO-3- secretion by the CCD is inhibited by incubation at low pH in vitro; this adaptation is initiated within 1 h of exposure to low pH, but requires an additional 2 h for significant expression. The decrease in HCO-3- secretion requires de novo protein synthesis and integrity of the microfilaments. Because the decrement in HCO-3- secretion was not associated with an increase in HCO-3- absorption, it is unlikely that beta-intercalated cells reverse their functional polarity in this model of metabolic acidosis.