McCann J D, Matsuda J, Garcia M, Kaczorowski G, Welsh M J
Howard Hughes Medical Institute, Department of Physiology, University of Iowa, College of Medicine, Iowa City 52242.
Am J Physiol. 1990 Jun;258(6 Pt 1):L334-42. doi: 10.1152/ajplung.1990.258.6.L334.
In airway epithelia, adenosine 3',5'-cyclic monophosphate (cAMP) stimulates Cl- secretion by activating apical membrane Cl- channels and basolateral membrane K+ channels. Cl- channels are regulated by cAMP-dependent phosphorylation, whereas K+ channels are regulated by the cytosolic Ca2+ concentration, [Ca2+]c. Our recent observation that cAMP increases [Ca2+]c suggested that cAMP might indirectly regulate K+ channels by increasing [Ca2+]c. To study regulation of K+ channels we measured 86Rb efflux, single K+ channels in membrane patches, and [Ca2+]c with the fluorescent indicator fura-2. Isoproterenol and Ca2+ ionophore, A23187, transiently increased [Ca2+]c and transiently stimulated 86Rb efflux. Stimulation of 86Rb efflux resulted from release of intracellular Ca2+ stores. 86Rb efflux was blocked by Ba2+ or charybdotoxin, but not by tetraethylammonium. Charybdotoxin prevented all of the 86Rb efflux that was stimulated by A23187 or by forskolin. Charybdotoxin also blocked the low-conductance inwardly rectifying K+ channel (KCLIC) in membrane patches. These results indicate that the KCLIC channel is responsible for the Ca2(+)-dependent increase in K+ permeability in airway epithelial cells. They also indicate that cAMP-induced release of intracellular Ca2+ is sufficient to activate K+ channels.
在气道上皮细胞中，3',5'-环磷酸腺苷（cAMP）通过激活顶端膜氯离子通道和基底外侧膜钾离子通道来刺激氯离子分泌。氯离子通道受cAMP依赖性磷酸化调节，而钾离子通道受胞质钙离子浓度[Ca2+]c调节。我们最近观察到cAMP会增加[Ca2+]c，这表明cAMP可能通过增加[Ca2+]c间接调节钾离子通道。为了研究钾离子通道的调节，我们用荧光指示剂fura-2测量了86Rb外流、膜片上的单个钾离子通道以及[Ca2+]c。异丙肾上腺素和钙离子载体A23187可短暂增加[Ca2+]c并短暂刺激86Rb外流。86Rb外流的刺激是由于细胞内钙库的释放。86Rb外流被Ba2+或蝎毒素阻断，但不被四乙铵阻断。蝎毒素可阻止A23187或福斯可林刺激的所有86Rb外流。蝎毒素还可阻断膜片中的低电导内向整流钾离子通道（KCLIC）。这些结果表明，KCLIC通道负责气道上皮细胞中钾离子通透性的钙依赖性增加。它们还表明，cAMP诱导的细胞内钙释放足以激活钾离子通道。
