Dept. of Pharmacology, Harbin Med. Univ., Harbin 150086, China.
Am J Physiol Renal Physiol. 2011 Apr;300(4):F906-13. doi: 10.1152/ajprenal.00617.2010. Epub 2011 Jan 5.
The basolateral 50-pS K channels are stimulated by a cAMP-dependent pathway and inhibited by cytochrome P-450-omega-hydroxylase-dependent metabolism of arachidonic acid (AA) in the rat thick ascending limb (TAL). We now used the patch-clamp technique to examine whether stimulation of adenosine A(₂a) receptor modulates the inhibitory effect of AA on the basolateral 50-pS K channels in the medullary TAL. Stimulation of adenosine A(₂a) receptor with CGS-21680 or inhibition of phospholipase A₂ (PLA₂) with AACOCF3 increased the 50-pS K channel activity in the TAL. Western blot demonstrated that application of CGS-21680 decreased the phosphorylation of PLA(2) at serine residue 505, an indication of inhibiting PLA₂ activity. In the presence of CGS-21680, inhibition of PLA₂ had no further effect on the basolateral 50-pS K channels. The possibility that CGS-21680-induced stimulation of the basolateral 50-pS K channels was partially achieved by inhibition of PLA₂ in the TAL was also supported by the observation that CGS-21680 had no additional effect in the presence of AACOCF3. Moreover, stimulation of adenosine A(₂a) receptor with CGS-21680 also abolished the inhibitory effect of AA and 20-hydroxyeicosatetraenoic acid (20-HETE) on the 50-pS K channels. The effect of CGS-21680 on AA and 20-HETE-mediated inhibition of the 50-pS K channels was mediated by cAMP because application of membrane-permeable cAMP analog, dibutyryl-cAMP, not only increased the 50-pS K channel activity but also abolished the inhibitory effect of AA and 20-HETE. We conclude that stimulation of adenosine A(₂a) receptor increased the 50-pS K channel activity in the TAL, an effect that is achieved by suppression of PLA₂ activity and 20-HETE-induced inhibition.
基底外侧 50-pS K 通道被 cAMP 依赖性途径刺激，并被细胞色素 P-450-ω-羟化酶依赖的花生四烯酸 (AA) 代谢抑制，在大鼠升支粗段 (TAL) 中。我们现在使用膜片钳技术来研究腺苷 A₂a 受体的刺激是否调节 AA 对髓质 TAL 基底外侧 50-pS K 通道的抑制作用。用 CGS-21680 刺激腺苷 A₂a 受体或用 AACOCF3 抑制磷脂酶 A₂ (PLA₂) 增加了 TAL 中的 50-pS K 通道活性。Western blot 表明，CGS-21680 的应用降低了丝氨酸残基 505 处的 PLA₂磷酸化，表明 PLA₂活性受到抑制。在 CGS-21680 的存在下，PLA₂的抑制对基底外侧 50-pS K 通道没有进一步的影响。在 CGS-21680 存在下，PLA₂ 诱导的刺激对基底外侧 50-pS K 通道的部分作用是通过抑制 TAL 中的 PLA₂来实现的，这一观察结果也得到了支持，即 CGS-21680 在 AACOCF3 的存在下没有额外的作用。此外，用 CGS-21680 刺激腺苷 A₂a 受体也消除了 AA 和 20-羟二十碳四烯酸 (20-HETE) 对 50-pS K 通道的抑制作用。CGS-21680 对 AA 和 20-HETE 介导的 50-pS K 通道抑制作用是由 cAMP 介导的，因为应用膜通透 cAMP 类似物二丁酰基-cAMP，不仅增加了 50-pS K 通道活性，而且消除了 AA 和 20-HETE 的抑制作用。我们得出结论，刺激腺苷 A₂a 受体增加了 TAL 中的 50-pS K 通道活性，这种作用是通过抑制 PLA₂ 活性和 20-HETE 诱导的抑制来实现的。
