Cortisol alters carbonic anhydrase-mediated renal sulfate secretion

Abstract

Active transepithelial sulfate secretion rate by winter flounder renal proximal tubule epithelium in primary culture (fPTC) is dependent on intracellular carbonic anhydrase (CA) and enhanced by cortisol. To further evaluate this relationship, a partial cDNA clone (327 bp) of carbonic anhydrase II (CAII) with high sequence similarity to CAII from numerous species including fish, chicken, and human was obtained from fPTCs. The majority of CA activity and CAII protein was present in the cytosol of fPTCs; however, significant amounts of both (in addition to SDS-resistant CA activity, i.e., CAIV-like isoform) were present in concentrated plasma membranes. CAII from concentrated membranes migrated differently than purified CAII on nondenaturing PAGE gels, suggesting that CAII associates with another membrane component. Treatment of fPTCs with the cell-soluble CA inhibitor methazolamide (100 microM) caused a 58% reduction in active transepithelial SO4(2-) secretion. fPTCs that were previously cultured under high-cortisol concentrations, when subjected to 5 days of low physiological levels of cortisol, had decreased CA activity (28%), CAII protein abundance (65%), and net active SO4(2-) secretion (28%), with no effect on epithelial differentiation. Methazolamide and low-cortisol treatment in combination inhibited net active SO4(2-) secretion 56%, which was not different than the effect of methazolamide treatment alone. These data indicate that cortisol directly increases renal CA activity, CAII protein abundance, and CA-dependent SO4(2-) secretion in the marine teleost renal proximal tubule.

Role of tubular secretion and carbonic anhydrase in vertebrate renal sulfate excretion

“…Renal tubular CA activity is elevated 78% in rabbits undergoing metabolic acidosis, and increased renal acid excretion accompanies the induction of CA activity (14). As noted above, small changes in CA activity induced by cortisol alter the CA-dependent fraction of tubular SO 4 2Ϫ secretion (61). If…”

“…A portion of CAII (329 bp) was recently cloned from the winter flounder proximal tubule, and CAII protein was shown to be both cytosolic and membrane associated (61). Furthermore, CAII protein migrated differently than purified bovine 4.…”

“…Cortisol has recently been shown to alter CA expression in flounder PTCs (61). Control flounder PTCs were supplemented with high levels of cortisol (7.3 ϫ 10 Ϫ6 M), and removal of cortisol for 5 days resulted in cortisol concentrations (6.3 ϫ 10 Ϫ9 M) at the lower end of the physiological range (8.4 ϫ 10 Ϫ9 -3.5 ϫ 10 Ϫ7 M).…”

Carbonic anhydrase and acid–base regulation in fish

“…Indeed, until the finding of CA-mediated SO 4 2-excretion (Renfro et al, 1999), it was believed that the kidney of marine fish lacked CA activity entirely. Although relatively few species have been examined, the available data derived from studies using isolated tubules or employing immunocytochemistry suggest that CA is present in the kidneys of both marine and freshwater fish (Renfro et al, 1999;Pelis et al, 2003;Pelis and Renfro, 2004;Georgalis et al, 2006a;Gilmour et al, 2007a). The predominant CA isoform in trout kidney is the general cytosolic variant (tCAc) (Esbaugh et al, 2005).…”

“…Although previous studies have reported the presence of 'CA II' in fish kidney [e.g. Osorezan dace (Hirata et al, 2003); winter flounder (Pleuronectes americanus) (Pelis et al, 2003)], this renal CA is probably more appropriately termed cytosolic CA ('c' or 'a' nomenclature; see above). In trout and flounder, cytosolic CA is found within proximal tubules where it immunolocalizes to the cytosol and brush border membranes (Pelis and Renfro, 2004;Georgalis et al, 2006a) (Fig.…”