Koh S D, Dick G M, Sanders K M
Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno 89557, USA.
Am J Physiol. 1997 Dec;273(6):C2010-21. doi: 10.1152/ajpcell.1997.273.6.C2010.
The patch-clamp technique was used to determine the ionic conductances activated by ATP in murine colonic smooth muscle cells. Extracellular ATP, UTP, and 2-methylthioadenosine 5'-triphosphate (2-MeS-ATP) increased outward currents in cells with amphotericin B-perforated patches. ATP (0.5-1 mM) did not affect whole cell currents of cells dialyzed with solutions containing ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. Apamin (3 x 10(-7) M) reduced the outward current activated by ATP by 32 +/- 5%. Single channel recordings from cell-attached patches showed that ATP, UTP, and 2-MeS-ATP increased the open probability of small-conductance, Ca(2+)-dependent K+ channels with a slope conductance of 5.3 +/- 0.02 pS. Caffeine (500 microM) enhanced the open probability of the small-conductance K+ channels, and ATP had no effect after caffeine. Pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid tetrasodium (PPADS, 10(-4) M), a nonselective P2 receptor antagonist, prevented the increase in open probability caused by ATP and 2-MeS-ATP. PPADS had no effect on the response to caffeine. ATP-induced hyperpolarization in the murine colon may be mediated by P2y-induced release of Ca2+ from intracellular stores and activation of the 5.3-pS Ca(2+)-activated K+ channels.
采用膜片钳技术测定ATP激活的小鼠结肠平滑肌细胞的离子电导。在两性霉素B穿孔膜片的细胞中，细胞外ATP、UTP和2-甲硫基腺苷5'-三磷酸（2-MeS-ATP）增加外向电流。ATP（0.5-1 mM）对用含乙二醇双（β-氨基乙醚）-N，N，N'，N'-四乙酸的溶液透析的细胞的全细胞电流没有影响。蜂毒明肽（3×10⁻⁷ M）使ATP激活的外向电流降低32±5%。细胞贴附膜片的单通道记录显示，ATP、UTP和2-MeS-ATP增加了小电导、Ca²⁺依赖性K⁺通道的开放概率，其斜率电导为5.3±0.02 pS。咖啡因（500 μM）增加了小电导K⁺通道的开放概率，且ATP在咖啡因作用后无影响。磷酸吡哆醛6-偶氮苯基-2'，4'-二磺酸四钠（PPADS，10⁻⁴ M），一种非选择性P2受体拮抗剂，可阻止ATP和2-MeS-ATP引起的开放概率增加。PPADS对咖啡因反应无影响。ATP诱导的小鼠结肠超极化可能由P2y诱导的细胞内钙库释放Ca²⁺和激活5.3-pS Ca²⁺激活的K⁺通道介导。
