Sodium+/Hydrogen + exchanger

Functionally, the Dl-like receptors (Dl, D5) are coupled to the G protein Gas and thus can stimulate adenylyl cyclase. The D2-like receptors (D2, D3, and D4) couple to pertussis toxin sensitive G proteins (Gai/0), and consequently inhibit adenylyl cyclase activity. While the Dl-like receptors almost exclusively signal through Gas-mediated activation of adenylyl cyclase, the D2-like receptors have been reported to modulate the activity of a plethora of signaling molecules and pathways. Many of these actions are mediated through the G(3y subunit. Some of these molecules and pathways include the calcium channels, potassium channels, sodium-hydrogen exchanger, arachidonic acid release, and mitogen-activated protein kinase pathways. 

The kidney contains the major site of renin synthesis, the juxtaglomerular cells in the wall of the afferent arteriole. From these cells, renin is secreted not only into the circulation but also into the renal interstitium. Moreover, the enzyme is produced albeit in low amounts by proximal tubular cells. These cells also synthesize angiotensinogen and ACE. The RAS proteins interact in the renal interstitium and in the proximal tubular lumen to synthesize angiotensin II. In the proximal tubule, angiotensin II activates the sodium/hydrogen exchanger (NHE) that increases sodium reabsorption. Aldosterone elicits the same effect in the distal tubule by activating epithelial sodium channels (ENaC) and the sodium-potassium-ATPase. Thereby, it also induces water reabsotption and potassium secretion. 

Approximate selectivity coefficients for the exchange of various cations for lithium ions on a sulphonated polystyrene, a typically strong acid resin, are given in Table 18.1. The values are relative to Li = 1.0. The selectivity coefficient between two ions is the ratio of their selectivities relative to lithium. Hence, for a sodium-hydrogen exchange ... 

NHE-1 (sodium/hydrogen exchanger) Depends on cell type and species Fluorescent labeling, found at nuclear membrane Liver and cardiomyocytes in R. norvegicus No (Bkaily et al. 2004)... 

SlFFERT W. Regulation of platdet function by sodium-hydrogen exchange. CatdiovascRes 29 160-166,1995. 

Table 6.1 System parameters and derived rate data for sodium-hydrogen exchange kinetics on a styrene sulfonate resin (12% DVB) - finite volume. (Data from C. E. Harland, Ph.D. Thesis, University of Leeds, 1972)... 

Figure 6.3 Interpretation of ion exchange rate data according to film diffusion theory (equation 6.21) for sodium-hydrogen exchange on a styrenesulfonate resin (12% DVB)...

SLC9 (6) Sodium/hydrogen exchangers NHE and smooth muscles Ubiquitous (intestine. 

Yasutake, M., Avkiran, M., 1995. Exacerbation of reperfusion arrhythmias by a I adrenergic stimulation a potential role for receptor mediated activation of sarcolemmal sodium-hydrogen exchange. Car-diovasc. Res. 29, 222-230. 

TABLE 13.1-1 Calculated Values of Kc for Sodium-Hydrogen Exchange for Sulfonaled PeJystyrene-DVB... 

Inhibition of sodium-hydrogen exchange in the proximal tubules resulting in the inhibition of hydrogen ion secretion and enhanced excretion of bicarbonate. 

TABLE 13.1-2 Calculated Values of for Sodium-Hydrogen Exchange for Varying Degrees of Saturation... 

HOE-642, a selective sodium-hydrogen exchange subtype 1 inhibitor (Scholz et al. 1995), when given at 1 iM together with tetrodotoxin (44 jiM) protected isolated rat hearts from ischaemic/reper-fusion injury and lowered creatine phosphokinase activity in the coronary effluent in comparison to that observed in the non-treated hearts (Eng et al. 1998). 

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