We examined the effect of norepinephrine (NE) on intracellular pH (pHi) and activity of Na+([Formula: see text]) in the isolated perfused kidney proximal tubule of Ambystoma, using single-barreled voltage and ion-selective microelectrodes. In control[Formula: see text] Ringer, addition of 10−6M NE to the bath reversibly depolarized the basolateral membrane potential ( V1), the luminal membrane potential ( V2), and the transepithelial potential difference ( V3) and increased pHiby 0.14 ± 0.02. These effects were mimicked by isoproterenol but were abolished after pretreatment with SITS or in the absence of CO2/[Formula: see text]. Removal of bath Na+depolarized V1and V2, hyperpolarized V3, and decreased pHi. These effects are largely mediated by the electrogenic Na+-([Formula: see text])ncotransporter. In the presence of NE, the effects of Na+removal on membrane potential differences and the rate of change of pHiwere significantly smaller. Reducing bath [Formula: see text] concentration from 10 to 2 mM at constant CO2(pH 6.8) depolarized V1and V2, decreased pHi, and lowered[Formula: see text]. These changes are also due to Na+-([Formula: see text])n. In the presence of NE, reducing bath [[Formula: see text]] caused a smaller depolarizations of V1and V2, and the rate of pHidecrease was significantly reduced. Our results indicate: 1) NE causes an increase in pHi; 2) the NE-induced alkalinization is mediated by a SITS-sensitive and[Formula: see text]-dependent transporter on the basolateral membrane; and 3) in the presence of NE, the reduced effects caused by basolateral[Formula: see text] changes or Na+removal are indicative of an inhibitory effect of NE on Na+-([Formula: see text])ncotransport.