Kramer R H, Mokkapatti R, Levitan E S
Center for Neurobiology and Behavior, Columbia University of Physicians and Surgeons, New York, NY 10032.
Pflugers Arch. 1994 Jan;426(1-2):12-20. doi: 10.1007/BF00374665.
Caffeine elicits physiological responses in a variety of cell types by triggering the mobilization of Ca2+ from intracellular organelles. Here we investigate the effects of caffeine on intracellular Ca2+ concentration ([Ca2+]i) and ionic currents in anterior pituitary cells (GH3) cells. Caffeine has a biphasic effect on Ca(2+)-activated K+ current [IK(Ca)]: it induces a transient increase superimposed upon a sustained inhibition. While the transient increase coincides with a rise in [Ca2+]i, the sustained inhibition of IK(Ca) is correlated with a sustained inhibition of the L-type Ca2+ current. The L-type Ca2+ current is also inhibited by other agents that mobilize intracellular Ca2+, including thyrotropin releasing hormone (TRH) and ryanodine, but in a matter distinct from caffeine. Unlike the caffeine effect, the TRH-induced inhibition "washes-out" under whole-cell patch-clamp conditions and is eliminated by intracellular Ca2+ chelators. Likewise, the ryanodine-induced inhibition desensitizes while the caffeine-induced inhibition does not. Simultaneous [Ca2+]i and Ca2+ current measurements show that caffeine can inhibit Ca2+ current without changing [Ca2+]i. Single-channel recordings show that caffeine reduces mean open time without affecting single-channel conductance of L-type channels. Hence the effects of caffeine on ion channels in GH3 cells are attributable both to mobilization of intracellular Ca2+ and to a direct effect on the gating of L-type Ca2+ channels.
咖啡因通过触发细胞内细胞器中Ca2+的动员，在多种细胞类型中引发生理反应。在此，我们研究咖啡因对垂体前叶细胞（GH3细胞）内Ca2+浓度（[Ca2+]i）和离子电流的影响。咖啡因对Ca(2+)激活的K+电流[IK(Ca)]具有双相作用：它在持续抑制的基础上诱导短暂增加。短暂增加与[Ca2+]i升高同时出现，而IK(Ca)的持续抑制与L型Ca2+电流的持续抑制相关。L型Ca2+电流也受到其他动员细胞内Ca2+的试剂抑制，包括促甲状腺激素释放激素（TRH）和ryanodine，但方式与咖啡因不同。与咖啡因的作用不同，TRH诱导的抑制在全细胞膜片钳条件下“洗脱”，并被细胞内Ca2+螯合剂消除。同样，ryanodine诱导的抑制会脱敏，而咖啡因诱导的抑制则不会。同时进行的[Ca2+]i和Ca2+电流测量表明，咖啡因可以在不改变[Ca2+]i的情况下抑制Ca2+电流。单通道记录表明，咖啡因缩短了平均开放时间，而不影响L型通道的单通道电导。因此，咖啡因对GH3细胞离子通道的影响既归因于细胞内Ca2+的动员，也归因于对L型Ca2+通道门控的直接作用。
