Cross talk of bumetanide-sensitive and HCO3--dependent transporters activated by IBMX in renal epithelial A6 cells.
We studied cAMP-dependent regulation of ion transport in aldosterone-untreated renal epithelial A6 cells by measuring short-circuit current (Isc). Biphasic increases in Isc, a transient phase followed by a sustained one, were elicited in response to 1 mm 3-isobutyl-1-methylxanthine (IBMX, an inhibitor of phosphodiesterase) which increased cytosolic cAMP concentration. IBMX increased the apical Cl- conductance. The sustained phase of Isc induced by IBMX was reduced by 50 microM bumetanide (Na+/K+/2 Cl- cotransporter inhibitor) or 100 microM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS, an inhibitor of Cl-/HCO3- exchanger). Under the normal condition, the inhibitory effect of bumetanide was much larger than that of DIDS. On the other hand, under a low Cl- condition, the effect of DIDS was more effective than that of bumetanide. Further, under a Cl--free condition Na+/HCO3- symporter contributed to the IBMX-generated Isc. Taken together, our observations suggest that in A6 cells (i) IBMX stimulates Cl- secretion associated with an increase in apical Cl- conductances, (ii) the ionic components to generate the IBMX-induced Isc are mainly maintained by bumetanide-sensitive Na+/K+/2 Cl- cotransporter and DIDS-sensitive Cl-/HCO3- exchanger, (iii) Cl-/HCO3- exchanger coupled to Na+/HCO3- symporter under a low-Cl- condition or Na+/HCO3- symporter under a Cl--free condition contributes to the IBMX-induced Isc, compensating for diminishment of the Na+/K+/2Cl- cotransporter-mediated Cl- secretion, (iv) IBMX increases Cl- and HCO3- conductances in the apical membrane.
Niisato
N
N
Laboratory for Cellular and Molecular Physiology, Division of Respiratory Research, Hospital for Sick Children Research Institute, University of Toronto, Toronto, Ontario, Canada, M5G 1X8.
Marunaka
Y
Y
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology*; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000818:Animals; D017920:Antiporters / Q000037:antagonists & inhibitors*; D001639:Bicarbonates / Q000378:metabolism; D002034:Bumetanide / Q000494:pharmacology*; D002460:Cell Line; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D004232:Diuretics / Q000494:pharmacology*; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D014982:Xenopus laevis
D017920:Antiporters; D001639:Bicarbonates; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D004232:Diuretics; D010726:Phosphodiesterase Inhibitors; D002034:Bumetanide; D000242:Cyclic AMP; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D015056:1-Methyl-3-isobutylxanthine