Cook D I, Wegman E A, Ishikawa T, Poronnik P, Allen D G, Young J A
Department of Physiology, University of Sydney, NSW, Australia.
Pflugers Arch. 1992 Feb;420(2):167-71. doi: 10.1007/BF00374986.
Since the secretory cells of the sheep parotid gland contain large numbers of high-conductance, voltage- and Ca(2+)-activated K+ channels (BK channels), we have used tetraethylammonium (TEA), a commonly employed blocker of BK channels, to investigate their role in secretion by this gland. In patch-clamp studies we found that 10 mmol/l TEA applied extracellularly inhibits the BK channel but not a 30-pS K+ channel also seen in this gland. We then showed by in-vivo perfusion that muscarinically evoked secretion is inhibited almost completely by 10 mmol/l TEA. We next used microspectrofluorimetry with fura-2 to demonstrate that muscarinic agonists cause the intracellular free Ca2+ concentration to increase. Unexpectedly, however, we found that 0.3-10 mmol/l TEA inhibited the increase in intracellular free Ca2+ induced by 5.0 mumol/l bethanechol or by 0.1 mumol/l acetylcholine. Consequently we conclude that the inhibition of muscarinically evoked secretion by the sheep parotid gland by TEA cannot be attributed solely to blockade of the BK channel--rather it must be attributed, at least in part, to blockade of some step in muscarinic signal transduction, for instance, receptor-agonist binding or Ca2+ release into the cytosol.
由于绵羊腮腺的分泌细胞含有大量高电导、电压和钙离子激活的钾通道（BK通道），我们使用了四乙铵（TEA），一种常用的BK通道阻滞剂，来研究其在该腺体分泌中的作用。在膜片钳研究中，我们发现细胞外施加10 mmol/L的TEA可抑制BK通道，但对该腺体中也存在的一种30 pS的钾通道无抑制作用。然后我们通过体内灌注表明，10 mmol/L的TEA几乎完全抑制了毒蕈碱诱发的分泌。接下来，我们使用fura-2进行显微荧光测定，以证明毒蕈碱激动剂可使细胞内游离钙离子浓度升高。然而，出乎意料的是，我们发现0.3 - 10 mmol/L的TEA可抑制由5.0 μmol/L氨甲酰甲胆碱或0.1 μmol/L乙酰胆碱诱导的细胞内游离钙离子浓度升高。因此，我们得出结论，TEA对绵羊腮腺毒蕈碱诱发分泌的抑制作用不能仅归因于BK通道的阻断，而必须至少部分归因于毒蕈碱信号转导中某个步骤的阻断，例如受体 - 激动剂结合或钙离子释放到细胞质中。
