Paulais Marc, Lourdel Stéphane, Teulon Jacques
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.
Am J Physiol Renal Physiol. 2002 May;282(5):F866-76. doi: 10.1152/ajprenal.00238.2001.
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.
我们使用膜片钳技术研究了皮质厚升支（CTAL）基底外侧膜中钾离子通道的特性。在细胞贴附式膜片中，约34%含有内向整流钾离子通道（钾离子与钠离子通透率之比约为22），其内向电导（G(in)）为44 pS，外向电导（G(out)）约为10 pS（G(in)/G(out)约为4）。通道活性(NP(o))随去极化而增加。当外翻式膜片的胞质侧暴露于无镁离子的培养基中时，通道的G(in)为50 pS，内向整流作用较弱（G(in)/G(out)约为1）。胞质镁离子降低了G(out)，在1.3 mM镁离子浓度下G(in)/G(out)为3.8。胞内钠离子在20 mM钠离子浓度下也使G(in)/G(out)为1.6。精胺降低了外翻式膜片上的NP(o)。在去极化电压下对精胺的敏感性[半数最大抑制浓度(K(i)) = 0.2 microM]远高于超极化电压下（K(i) = 26 microM）。0.5 microM精胺导致半数失活时的钳制电位为43 mV，有效价为1.25。观察到浴液pH与外翻式膜片NP(o)之间呈S形关系，pK为7.6，希尔系数为1.8。细胞内酸化也降低了细胞贴附式膜片的NP(o)。该通道可能是CTAL基底外侧膜钾离子电导的主要成分。
