Electrogenic exchange

The malate-aspartate shuttle is the most important pathway for transferring reducing equivalents from the cytosol to the mitochondria in brain. This shuttle involves both the cytosolic and mitochondrial forms of aspartate aminotransferase and malate dehydrogenase, the mitochondrial aspartate-glutamate carrier and the dicarboxylic acid carrier in brain (Fig. 31-5) [69]. The electrogenic exchange of aspartate for glutamate and a... 

This discovery was followed by the description of the Ca ATPases, found both in intracellular membranes, such as the sarcoplasmic reticulum (SERCA ATPases), and on the plasma membrane (PM Ca ATPases). These are also considered to be electrogenic, exchanging 2Ca for 2H. The PM Ca ATPases are uniquely regulated by the binding of calmodulin to the C-terminal region of this single-subunit enzyme. 

Electrogenic antiport, ADP uptake favored by the membrane potential can also mediate electroneutral exchange of ADPout for... 

Modulation of electrogenic Na/Ca exchange current by oxygen radical generating systems in isolated guinea pig ventricular myocytes. J. Mol. Cell. Cardiol. 24 (Suppl V), S28. 

Figure 15.2 Ion transporters in human vaginal-ectocervical epithelial cells, sorted into the apical and basolateral domains of the plasma membrane. Black solid symbols depict electrogenic transporters hatched symbols depict electroneutral transporters. Squares are tight junctions. MCT—monocarboxylate transporter NBC— Na+/HCO co-transporter AE—acid (Cl /HCOj ) exchanger NHE (types 1 or 3)—Na+/H+ exchangers.

Calcium may also be taken up by Na+-Ca2t exchange. Thus sperm plasma membranes take up Ca2+ by an ATP-independent Na+/Ca2+ antiporter. Ejaculated sperm cannot do this, due to the presence of a protein" that binds strongly to the plasma membrane.170 A highly active, electrogenic Na+/Ca2+ exchange occurs in sarcolemmal vesicles from cardiac muscle.171... 

Scheel O, Zdebik AA, Lourdel S, Jentsch TJ. 2005. Voltage-dependent electrogenic chloride/proton exchange by endosomal CLC proteins. Nature 436 424—7. 

Assuming then a Na+ concentration ratio of 10, the Na+/H+ exchanger could achieve a pHi value 1 unit higher than pHo. The fact that such a steady state pHi value is rarely observed indicates that the activity of the exchanger is counterbalanced by cell acidifying mechanisms such as electrogenic membrane leaks for acid equivalents (H+, OH-, HCO3 ) and the metabolic production of H+. 

At least three types of ATP driven H+ pumps may be potentially involved in the regulation of pHi. These are (a) an electrogenic H+ translocating ATPase found in the mammalian distal nephron (b) an electroneutral K+-H+ exchange ATPase that is responsible for acid secretion by gastric cells and (c) a vacuolar H+-ATPase which is responsible for the low pH of endocytic vesicles. The vacuolar H+-ATPase can be inhibited by the macrolide antibiotic bafilomycin Al. The gastric K+-H+-ATPase is inhibited by antiulcer drugs such as omeprazole. 

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