Barium- or quinine-induced depolarization activates K+, Na+ and cationic conductances in frog proximal tubular cells.
1. Frog proximal tubular cells were fused into giant cells. We measured membrane potential (Vm), its changes (delta Vm), and current-induced voltage changes (delta psi) in single cells, during control and experimental states. Each cell served as its own control. 2. In the presence of a physiological Ringer solution, the transference number for potassium (tK) was 0.50. Barium (3 mM) reduced membrane conductance (Gm) by 50%; low-Cl- solutions and low-Na+ solutions also diminished Gm, by 52 and 30%, respectively. The association of barium and low-NaCl solutions decreased Gm to approximately 38% of control, indicating that the impermeant substitute of a physiological ion may interact with other pathways; alternatively, blockade of steady-state conductances may activate physiologically silent processes. 3. In an attempt to enhance the contribution of the partial K+ conductance (GK) to Gm, fused cells were exposed to low-Cl- solutions, containing in addition 0.1 mM-methazolamide, to inhibit the rheogenic Na(+)-HCO3-symport, and 1 microM-amiloride, to block Na+ conductance (GNa). tK went up to 0.83. 4. The high tK preparation was challenged with barium (3 mM) or quinine (Quin, 1 mM). These blockers produced large depolarizations (approximately 60 mV), however, although Gm decreased along early- and mid-depolarization, Gm plateaued and eventually it increased with larger and larger depolarization. 5. Depolarization-associated increase in Gm reflects activation of other conductances. These are Na+, cationic, and K+ conductance(s) poorly sensitive to quinine or barium. In the presence of Ba(2+)- or Quin-induced depolarization, injection of depolarizing current produces delayed increase in conductance. 6. Depolarization-induced activation of cationic conductance (Gcat) and GNa results in enlargement of the K+ electrochemical potential difference, to about 70 mV; this difference allows recycling of K+ ions outwards, since a GK is still detected and may contribute up to 38% of the total conductance.
Discala
F
F
INSERM U.323, Faculté de Médecine Necker Enfants-Malades, Paris, France.
Belachgar
F
F
Planelles
G
G
Hulin
P
P
Anagnostopoulos
T
T
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology*; D007687:Kidney Tubules, Proximal / Q000378:metabolism* / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D008704:Methazolamide / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects; D011803:Quinine / Q000494:pharmacology*; D011895:Rana ridibunda; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects
D015221:Potassium Channels; D001464:Barium; D000584:Amiloride; D012964:Sodium; D011803:Quinine; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium; D008704:Methazolamide