Acid-induced two-step depolarization in the peritubular membrane of bullfrog kidney proximal tubules.
Using ion-selective microelectrode technique, we investigated acid-induced changes of peritubular membrane potential (EM) and intracellular activity of Na+ and H+ ((Na)i and pHi) in the proximal tubule of perfused bullfrog kidney in vivo. When peritubular pH was reduced at constant PCO2, EM was depolarized in two steps: i.e., an initial sharp fall followed by an additional deeper fall. This was termed as the acid-induced two-step depolarization. During this change, pHi was decreased gradually from 7.4 to 6.9 in response to 1/10 HCO3- reduction (pH from 7.7 to 6.7), whereas (Na)i was increased after a transient decrease. This result supports the peritubular rheogenic HCO3- exit coupled to Na+ movement during the initial depolarization period. Complete removal of peritubular HCO3- at constant pH produced a less marked initial depolarization with a transient rise of pHi, followed by a partial repolarization without appreciable change in (Na)i. Peritubular SITS administration inhibited these depolarization responses to the acid perfusion. The above findings suggest that 1) the initial part of the two-step EM depolarization produced by low HCO3- or HCO(3-)-free perfusion resulted mainly from the peritubular rheogenic exist of HCO3-, 2) the magnitude of initial depolarization would also be affected by pHi, and 3) the subsequent delayed changes of EM were mainly determined by the pHi-sensitive K+ conductance of the peritubular membrane.
Kubokawa
M
M
Department of Physiology, Osaka Medical College, Takatsuki, Japan.
Kubota
T
T
Kotera
K
K
Fujimoto
M
M
D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000143:Acids; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D004553:Electric Conductivity; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D010477:Perfusion; D011188:Potassium / Q000378:metabolism; D011892:Rana catesbeiana; D012964:Sodium / Q000378:metabolism
D000143:Acids; D001639:Bicarbonates; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D012964:Sodium; D011188:Potassium