Functional properties of the rat Na/H exchanger NHE-2 isoform expressed in Na/H exchanger-deficient Chinese hamster ovary cells.

摘要: Abstract The primary structure and functional expression of the rat Na/H exchanger (NHE) NHE-2 isoform has recently been reported (Wang, Z., Orlowski, J., Shull, G. E. (1993) J. Biol. Chem. 268, 11925-11928). To further characterize some its properties, biochemical pharmacological analyses were performed on exchanger-deficient Chinese hamster ovary cells (AP-1) that had stably transfected with a full-length cDNA. Transport activity for was assayed by measuring amiloride-inhibitable 22Na+ influx following an acute intracellular acid load. Pharmacological revealed relatively high affinity amiloride analogues. most potent analogue 5-(N-ethyl-N-isopropyl)amiloride (EIPA) (K0.5 = 79 nM), followed 5-(N,N-dimethyl)amiloride (DMA) 250 1.4 microM), benzamil 320 microM). Nonamiloride compounds known to inhibit other isoforms also inhibited order potency: clonidine 42 microM) > harmaline 330 approximately cimetidine Biochemical showed extracellular Na+ dependence simple, saturating Michaelis-Menten kinetics apparent constant (KNa) 50 mM. In contrast, H+ appeared activate positive cooperative mechanism half-maximal activation value pK 6.90. Other cations, such as Li+ H+, acted competitive inhibitors NHE-2, Ki values 3.0 mM 10 nM, respectively. K+ no effect transport NHE-2. These results indicated cDNA encodes distinct properties compared NHE-1 -3.