Depolarization-induced alkalinization in proximal tubules. I. Characteristics and dependence on Na+.
We used intracellular pH-sensitive and voltage microelectrodes to examine the effects of depolarization on intracellular pH (pHi) in isolated perfused proximal tubules from the tiger salamander Ambystoma tigrinum. Tubules were depolarized by raising [K+] in the bath (b) or lumen (l), or by adding Ba2+ (1 mM) to the bath or lumen, always in nominally HCO3-free solutions. Increasing [K+]b from 2.5 to 50 mM caused the basolateral membrane to depolarize by an average of 45 mV, and pHi to increase by 0.23 over 3 min. Similar alkalinization was observed when basolateral Ba2+ (1 mM) was used to depolarize the cell at constant extracellular [K+], suggesting that the alkalinization observed during exposure to elevated [K+]b results from depolarization rather than an increase in [K+]b. The initial rate of depolarization-induced alkalinization (DIA) was proportional to the magnitude of the depolarization, regardless of whether tubules were depolarized by elevated [K+]b, elevated [K+]l, or by basolateral Ba2+. An exception was the initial rate of the alkalinization caused by 1 mM luminal Ba2+, which was more than 10-fold greater than that predicted from the depolarization. The voltage and pHi responses to basolateral Ba2+ were smaller in some tubules than others, as were the responses to elevated [K+]l. Tubules with small responses to 1 mM [Ba2+]b had large responses to 50 mM [K+]l, whereas tubules with large responses to 1 mM [Ba2+]b had small responses to 50 mM [K+]l. This variability can be accounted for by differences in the luminal K+ conductance. The DIA was partially inhibited by removal of Na+ from only the lumen or only the bath, but completely inhibited by bilateral Na+ removal. We conclude that the depolarization-induced alkalinization results from additive effects of Na+-dependent processes at both the luminal and basolateral membranes.
Siebens
A W
AW
Department of Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.
Boron
W F
WF
D000557:Ambystoma; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D005260:Female; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D010477:Perfusion; D011188:Potassium / Q000494:pharmacology*; D012964:Sodium / Q000494:pharmacology*
D001464:Barium; D012964:Sodium; D011188:Potassium