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Articles in PresS, published online ahead of print November 27, 2001
Am J Physiol Renal Physiol, 10.1152/ajprenal.00238.2001
Submitted on August 1, 2001
Accepted on November 23, 2001
1 INSERM U426, Paris, France
* To whom correspondence should be addressed. E-mail: paulais{at}bichat.inserm.fr.
We investigated the properties of K+ channels in the basolateral membrane of cortical thick ascending limb (CTAL) using the patch-clamp technique. Around 34% of cell-attached patches contained an inwardly rectifying K+ channel (PK+ /PNa+ ~ 22) having a inward conductance (Gin) of 44 pS and an outward conductance (Gout) of ~10 pS (Gin/Gout ~ 4). Channel activity (NPo) increased with depolarization. When the cytosol side of inside-out patches was exposed to an Mg2+-free medium, the channel had a Gin of 50 pS and was weakly inwardly rectifying (Gin/Gout ~ 1). Cytosolic Mg2+ reduced Gout, yielding a Gin/Gout of 3.8 at 1.3 mM Mg2+. Internal Na+ also yield a Gin/Gout of 1.6 at 20 mM Na+. Spermine reduced NPo on inside-out membrane patches. Sensitivity to spermine at depolarizing voltages (Ki = 0.2 µM) was much greater than at hyperpolarizing voltages (Ki = 26 µM). Half-inactivation by 0.5 µM spermine occurred at Vc = 43 mV, with an effective valence of 1.25. A sigmoid relationship between bath pH and NPo 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 NPo of cell-attached patches. This channel is probably a major component of K+ conductance in the CTAL basolateral membrane.
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