Endogenous Na(+)-K+ (or NH4+)-2Cl- cotransport in Rana oocytes; anomalous effect of external NH4+ on pHi.
AUTOR(ES)
Keicher, E
RESUMO
1. In Rana oocytes, measurements with chloride-sensitive microelectrodes show that the mean intracellular chloride activity (34.8 +/- 6.3 mM, n = 79) is three times higher than that expected for the passive distribution of chloride ions across the outer membrane (12.4 mM, mean membrane potential -43 +/- 8.8 mV, n = 79). 2. Reuptake of chloride into oocytes depleted by prolonged exposure to chloride-free saline takes place against the electrochemical gradient. 3. Chloride reuptake does not take place in sodium-free solution or in a sodium-substituted potassium-free solution. It is inhibited by bumetanide (10(-5) M) in the bathing medium. 4. The overall stoichiometry of the transport mechanism deduced from simultaneous measurements of intracellular sodium and chloride using ion-selective electrodes is 1Na+:1K+:2Cl-. 5. Ammonium ions substitute for potassium on the cotransporter. 6. In oocytes smaller than 0.9 mm in diameter, exposure to external ammonium causes an alkaline shift in intracellular pH as the NH3 enters and takes up H+ to form NH4+. We propose that chloride-dependent NH4+ transport contributes to the accumulation of NH4+ and causes the 'postexposure' acidification as the intracellular NH4+ releases H+ to form NH3 which is then lost from the cell. 7. In larger oocytes ammonium exposure produces a rapid reduction in pHi which may be explained in part by cotransport-mediated uptake of NH4+. Evidence is also provided for a second chloride-dependent NH4+ transport mechanism and a chloride-independent process.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1160354Documentos Relacionados
- Urea inhibits NaK2Cl cotransport in human erythrocytes.
- Microfilament-dependent activation of Na+/K+/2Cl- cotransport by cAMP in intestinal epithelial monolayers.
- Effect of NH4+ ions on phi 29 DNA-protein p3 replication: formation of a complex between the terminal protein and the DNA polymerase.
- Effect of glucose on pHi recovery in HEK-293 cells.
- Isoprenaline, Ca2+ and the Na(+)-K+ pump in guinea-pig ventricular myocytes.