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Barium‐ or quinine‐induced depolarization activates K+, Na+ and cationic conductances in frog proximal tubular cells.
Author(s) -
Discala F,
Belachgar F,
Planelles G,
Hulin P,
Anagnostopoulos T
Publication year - 1992
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1992.sp019055
Subject(s) - depolarization , barium , membrane potential , conductance , biophysics , chemistry , amiloride , sodium , biochemistry , inorganic chemistry , biology , mathematics , organic chemistry , combinatorics
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.