Cl--dependent and Cl--independent Na+/ HCO3- acid extrusion in cultured rat cerebellar astrocytes.
It is still uncertain whether the Na+-dependent Cl--HCO3- exchanger (NCBE) is expressed in mammalian astrocytes. Using fluorescent indicators to monitor the intracellular pH (pHi) and intracellular Na+ or Cl- levels, the NCBE in cultured rat cerebellar astrocytes was examined in detail. In nominally bicarbonate-free (Hepes-buffered) medium, a marked pHi recovery from internal acid load was seen which could be blocked completely by 30 microM HOE 694, a specific Na+-H+ exchanger isoform 1(NHE-1) inhibitor, at a pHi above 6.9. These conditions were therefore used to block NHE activity in CO2/HCO3-buffered media when the NCBE was being studied at pHi above 6.9. After internal acid loading in completely Cl--free bicarbonate-buffered medium (containing HOE 694), the rates of pHi recovery and transient Na+ influx were considerably slowed, and the Cl--dependent acid extrusion was both Na+- and 4,4-diisothiocyano-stilbene-disulphonic acid (DIDS)-sensitive. Moreover, a HCO3-dependent Cl- efflux during internal acid injection was seen. These results suggest that the NCBE is present in astrocytes. Following repetitive internal acid loading by addition of 5% CO2 to internal Cl- depleted cells, a similar rate of pHi recovery was consistently seen, suggesting Cl--independent pHi regulation also occurred in astrocytes. Moreover, this pHi recovery was completely blocked in the absence of sodium or on addition of DIDS, confirming that the Na+-HCO3 cotransporter (NBC) is present. Thus, the present study provides evidence that both the NCBE and NBC play important roles in acid extrusion in cultured mammalian astrocytes.
Ko
Y P
YP
Department of Physiology, College of Medicine, National Taiwan University, Taipei, ROC.
Lang
H J
HJ
Loh
S H
SH
Chu
K C
KC
Wu
M L
ML
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000143:Acids / Q000378:metabolism*; D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000378:metabolism*; D001639:Bicarbonates / Q000493:pharmacokinetics; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002021:Buffers; D002245:Carbon Dioxide / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology; D002712:Chlorides / Q000493:pharmacokinetics*; D005260:Female; D005456:Fluorescent Dyes; D005731:Ganglionic Stimulants / Q000494:pharmacology; D006146:Guanidines / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008297:Male; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000493:pharmacokinetics; D027982:Sodium-Bicarbonate Symporters; D013450:Sulfones / Q000494:pharmacology
D000143:Acids; D001639:Bicarbonates; D002021:Buffers; D002352:Carrier Proteins; D002712:Chlorides; D005456:Fluorescent Dyes; D005731:Ganglionic Stimulants; D006146:Guanidines; D000644:Quaternary Ammonium Compounds; D027982:Sodium-Bicarbonate Symporters; D013450:Sulfones; C074107:3-methylsulfonyl-4-piperidinobenzoyl guanidine; D002245:Carbon Dioxide; D012964:Sodium; C027917:tetramethylammonium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid