Wu W L, So S C, Sun Y P, Chung Y W, Grima J, Wong P Y, Yan Y C, Chan H C
Department of Physiology, Faculty of Medicine, Chinese University of Hong Kong, Shatin, Hong Kong, China.
Biochem Biophys Res Commun. 1998 Jul 30;248(3):728-32. doi: 10.1006/bbrc.1998.9051.
Previous study has demonstrated functional expression of a sperm Ca(2+)-activated K+ channel in Xenopus oocytes injected with RNAs from the rat testes. Using the same expression system, the present study investigated the specific purinoceptor subtype involved in mediating the effect of extracellular ATP. The effect of ATP on an outwardly rectifying current, previously demonstrated to be mediated by a "Maxi" Ca(2+)-activated K+ channel, was compared to the current responses to different nucleotides using the two-electrode voltage-clamp technique. An order of relative effectiveness appeared to be UTP > ATP > ADP > adenosine, consistent with the pharmacological classification of P2U receptors. ATP was also found to exert an inhibitory effect on the Ca(2+)-activated K+ current, elicited by the Ca2+ ionophore ionomycin. A similar inhibitory effect was observed with UTP, again suggesting the involvement of P2U receptor. RT-PCR study also confirmed the expression of P2U receptor mRNA in isolated spermatogenic cells. The present results demonstrate the expression of P2U receptor and its dual role, both stimulatory and inhibitory, in the modulation of the Ca(2+)-activated K+ channel in spermatogenic cells. The present finding lends support to an important role of extracellular ATP in sperm functions.
先前的研究已证明，在注射了来自大鼠睾丸RNA的非洲爪蟾卵母细胞中，精子钙激活钾通道有功能性表达。利用相同的表达系统，本研究调查了介导细胞外ATP作用的特定嘌呤受体亚型。使用双电极电压钳技术，将ATP对先前证明由“大电导”钙激活钾通道介导的外向整流电流的作用，与对不同核苷酸的电流反应进行比较。相对效力顺序似乎为UTP > ATP > ADP > 腺苷，这与P2U受体的药理学分类一致。还发现ATP对由钙离子载体离子霉素引发的钙激活钾电流有抑制作用。UTP也观察到类似的抑制作用，再次表明P2U受体的参与。RT-PCR研究也证实了P2U受体mRNA在分离的生精细胞中的表达。目前的结果证明了P2U受体的表达及其在生精细胞中对钙激活钾通道调节的双重作用，即刺激和抑制作用。目前的发现支持了细胞外ATP在精子功能中的重要作用。
