Properties of an inwardly rectifying K(+) channel in the basolateral membrane of mouse TAL.
We investigated the properties of K(+) channels in the basolateral membrane of the cortical thick ascending limb (CTAL) using the patch-clamp technique. Approximately 34% of cell-attached patches contained an inwardly rectifying K(+) channel (K(+)-to-Na(+) permeability ratio approximately 22), having an inward conductance (G(in)) of 44 pS and an outward conductance (G(out)) of approximately 10 pS (G(in)/G(out) approximately 4). Channel activity (NP(o)) increased with depolarization. When the cytosolic sides of inside-out patches were exposed to an Mg(2+)-free medium, the channel had a G(in) of 50 pS and was weakly inwardly rectifying (G(in)/G(out) approximately 1). Cytosolic Mg(2+) reduced G(out), yielding a G(in)/G(out) of 3.8 at 1.3 mM Mg(2+). Internal Na(+) also yielded a G(in)/G(out) of 1.6 at 20 mM Na(+). Spermine reduced NP(o) on inside-out membrane patches. Sensitivity to spermine at depolarizing voltages [half-maximal inhibitory concentration (K(i)) = 0.2 microM] was much greater than at hyperpolarizing voltages (K(i) = 26 microM). Half-inactivation by 0.5 microM spermine occurred at a clamp potential of 43 mV, with an effective valence of 1.25. A sigmoid relationship between bath pH and NP(o) of inside-out membrane patches was observed, with a pK of 7.6 and a Hill coefficient of 1.8. Intracellular acidification also reduced the NP(o) of cell-attached patches. This channel is probably a major component of K(+) conductance in the CTAL basolateral membrane.
Paulais
Marc
M
Institut National de la Santé et de la Recherche Médicale U.426, Institut Fédératif de Recherche 02, Faculté de Médecine Xavier Bichat, Université Paris 7, 75018 Paris, France. paulais@bichat.inserm.fr
Lourdel
Stéphane
S
Teulon
Jacques
J
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D002462:Cell Membrane / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D004553:Electric Conductivity; D006863:Hydrogen-Ion Concentration; D008138:Loop of Henle / Q000502:physiology* / Q000648:ultrastructure*; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials; D051379:Mice; D008813:Mice, Inbred ICR; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects / Q000502:physiology*; D012964:Sodium / Q000494:pharmacology; D013096:Spermine / Q000494:pharmacology
D002614:Chelating Agents; D024661:Potassium Channels, Inwardly Rectifying; D013096:Spermine; D000255:Adenosine Triphosphate; D004492:Edetic Acid; D012964:Sodium; D008274:Magnesium