Mechanisms of ammonia and ammonium transport by rhesus-associated glycoproteins.
In this study we characterized ammonia and ammonium (NH3/NH4(+)) transport by the rhesus-associated (Rh) glycoproteins RhAG, Rhbg, and Rhcg expressed in Xenopus oocytes. We used ion-selective microelectrodes and two-electrode voltage clamp to measure changes in intracellular pH, surface pH, and whole cell currents induced by NH3/NH4(+) and methyl amine/ammonium (MA/MA(+)). These measurements allowed us to define signal-specific signatures to distinguish NH3 from NH4(+) transport and to determine how transport of NH3 and NH4(+) differs among RhAG, Rhbg, and Rhcg. Our data indicate that expression of Rh glycoproteins in oocytes generally enhanced NH3/NH4(+) transport and that cellular changes induced by transport of MA/MA(+) by Rh proteins were different from those induced by transport of NH3/NH4(+). Our results support the following conclusions: 1) RhAG and Rhbg transport both the ionic NH4(+) and neutral NH3 species; 2) transport of NH4(+) is electrogenic; 3) like Rhbg, RhAG transport of NH4(+) masks NH3 transport; and 4) Rhcg is likely to be a predominantly NH3 transporter, with no evidence of enhanced NH4(+) transport by this transporter. The dual role of Rh proteins as NH3 and NH4(+) transporters is a unique property and may be critical in understanding how transepithelial secretion of NH3/NH4(+) occurs in the renal collecting duct.
Section of Nephrology, Department of Medicine, and Department of Physiology, Southeast Louisiana Veterans Health Care System, New Orleans, Louisiana; and Tulane Hypertension and Renal Center of Excellence, Tulane University School of Medicine, New Orleans, Louisiana.
Tolga
T
Caner
Section of Nephrology, Department of Medicine, and Department of Physiology, Southeast Louisiana Veterans Health Care System, New Orleans, Louisiana; and Tulane Hypertension and Renal Center of Excellence, Tulane University School of Medicine, New Orleans, Louisiana.
Solange
S
Abdulnour-Nakhoul
Section of Nephrology, Department of Medicine, and Department of Physiology, Southeast Louisiana Veterans Health Care System, New Orleans, Louisiana; and Tulane Hypertension and Renal Center of Excellence, Tulane University School of Medicine, New Orleans, Louisiana.
Karen
K
Brown
Section of Nephrology, Department of Medicine, and Department of Physiology, Southeast Louisiana Veterans Health Care System, New Orleans, Louisiana; and Tulane Hypertension and Renal Center of Excellence, Tulane University School of Medicine, New Orleans, Louisiana.
M Toriqul
MT
Islam
Section of Nephrology, Department of Medicine, and Department of Physiology, Southeast Louisiana Veterans Health Care System, New Orleans, Louisiana; and Tulane Hypertension and Renal Center of Excellence, Tulane University School of Medicine, New Orleans, Louisiana.
L Lee
LL
Hamm
Section of Nephrology, Department of Medicine, and Department of Physiology, Southeast Louisiana Veterans Health Care System, New Orleans, Louisiana; and Tulane Hypertension and Renal Center of Excellence, Tulane University School of Medicine, New Orleans, Louisiana nakhoul@tulane.edu.
Nazih L
NL
Nakhoul
D000641:Ammonia / Q000378:metabolism*; D064751:Ammonium Compounds / Q000378:metabolism*; D000818:Animals; D005260:Female; D006023:Glycoproteins / Q000378:metabolism; D017136:Ion Transport / Q000502:physiology; D008562:Membrane Glycoproteins / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D014982:Xenopus laevis
D064751:Ammonium Compounds; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D000641:Ammonia
Rh glycoproteins; RhAG; Rhbg; Rhcg; ammonia transport; pH regulation