Hirsch J R, Schlatter E
Medizinische Poliklinik, Westfälische Wilhelms-Universität Münster, Federal Republic of Germany.
Wien Klin Wochenschr. 1997 Jun 27;109(12-13):485-8.
In the cortical collecting duct of the rat two Ca(2+)-dependent K+ channels have been described so far. In the luminal membrane a maxi K+ channel with a single channel conductance of 139 +/- 3 pS in excised membrane patches (n = 91) at 0 mV clamp voltage and asymmetrical KCl-concentrations in pipette and bath was found, while in the basolateral membrane an intermediate conductance K+ channel (85 +/- 1 pS, n = 53) and a small K+ channel (28 +/- 2 pS, n = 15) was described. All these K+ channels had similar pharmacological properties since all could be blocked by the K+ channel inhibitors Ba2+, TEA+, and charybdotoxin. Verapamil, known as a L-type Ca2+ channel blocker, was also capable of inhibiting these K+ channels. While the maxi K+ channel from the luminal membrane was upregulated by intracellular Ca2+ (EC50: 5 microM), the small and the intermediate K+ channel from the basolateral membrane were downregulated (IC50: 10 microM). When the cytosolic Ca(2+)-activity was in the physiological range below 1 microM the activity of the maxi K+ channel was low and regulated via intracellular pH and ATP. Furthermore, when CCD cells were strongly depolarized and under hypoosmotic stress, Ca2+ rose and activated this K+ channel, indicating that this channel is involved in volume regulation. Like the maxi K+ channel the intermediate conductance K+ channel from the basolateral membrane was also sensitive to intracellular changes of pH where acidic pH inhibited while alkaline pH activated this channel. But unlike the K+ channels from the luminal membrane the K+ channel from the basolateral membrane is not regulated by ATP up to 5 mM. The activity of the K+ channels from the basolateral membrane decreased steadily after excision of the membrane. This decrease could be prevented by applying cGMP and MgATP to the bath and thus, activating a membrane-bound cGMP-dependent protein kinase (PKG). The activation of the PKG could be reversed by its specific inhibitor KT5823 (1 microM). Due to the opposite regulation via intracellular Ca2+ and the involvement of different protein kinases a specific and independent regulation of K+ secretion and Na+ reabsorption is possible in the CCD of the rat.
迄今为止，在大鼠的皮质集合管中已发现两种钙依赖性钾通道。在管腔膜中，发现一种大电导钾通道，在0 mV钳制电压下，在切除的膜片（n = 91）中，其单通道电导为139±3 pS，移液管和浴槽中的氯化钾浓度不对称；而在基底外侧膜中，描述了一种中等电导钾通道（85±1 pS，n = 53）和一种小电导钾通道（28±2 pS，n = 15）。所有这些钾通道具有相似的药理学特性，因为它们都可被钾通道抑制剂钡离子、四乙铵离子和蝎毒素阻断。维拉帕米，一种已知的L型钙通道阻滞剂，也能够抑制这些钾通道。管腔膜中的大电导钾通道被细胞内钙上调（半数有效浓度：5微摩尔），而基底外侧膜中的小电导和中等电导钾通道被下调（半数抑制浓度：10微摩尔）。当胞质钙活性处于低于1微摩尔的生理范围内时，大电导钾通道的活性较低，并通过细胞内pH值和三磷酸腺苷进行调节。此外，当皮质集合管细胞强烈去极化并处于低渗应激状态时，钙升高并激活该钾通道，表明该通道参与容量调节。与大电导钾通道一样，基底外侧膜中的中等电导钾通道也对细胞内pH值变化敏感，酸性pH值抑制而碱性pH值激活该通道。但与管腔膜中的钾通道不同，基底外侧膜中的钾通道在高达5毫摩尔的三磷酸腺苷浓度下不受其调节。基底外侧膜中的钾通道活性在膜切除后稳步下降。通过向浴槽中加入环磷酸鸟苷和镁三磷酸腺苷，从而激活膜结合的环磷酸鸟苷依赖性蛋白激酶（蛋白激酶G），可以防止这种下降。蛋白激酶G的激活可被其特异性抑制剂KT5823（1微摩尔）逆转。由于通过细胞内钙的相反调节以及不同蛋白激酶的参与，在大鼠的皮质集合管中对钾分泌和钠重吸收进行特异性和独立调节是可能的。
