Hirooka Kazuyuki, Bertolesi Gabriel E, Kelly Melanie E M, Denovan-Wright Eileen M, Sun Xiaolu, Hamid Jawed, Zamponi Gerald W, Juhasz Alexander E, Haynes Lawrence W, Barnes Steven
Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 4H7.
J Neurophysiol. 2002 Jul;88(1):196-205. doi: 10.1152/jn.2002.88.1.196.
Human retinoblastoma cells are multipotent retinal precursor cells capable of differentiating into photoreceptors, neurons, and glia. The current-voltage relation of the undifferentiated cells is dominated by a transient inward current that disappears shortly after differentiation. In 20 mM Ba(2+)-containing bath solutions, the current has an activation midpoint near -25 mV and appears to be fully inactivated at -20 mV. Sr(2+) and Ca(2+) are preferred charge carriers relative to Ba(2+), and the current vanishes in the absence of these divalent cations. Cd(2+) blocks the current with an IC(50) of 160 microM, and Ni(2+) blocks in a biphasic manner with IC(50)s of 22 and 352 microM. The current is unaffected when sodium is replaced with other monovalent cations, and it is insensitive to nifedipine, omega-conotoxin GVIA, omega-agatoxin IVA, and omega-conotoxin MVIIC. RT-PCR revealed the presence of alpha 1G and alpha 1H mRNA in undifferentiated cells, but following differentiation, a striking reduction of both alpha 1G and alpha 1H mRNA was found, and this was paralleled by the loss of T-type Ca channel currents. alpha 1I subunit mRNA levels were low in undifferentiated and differentiated cells. These results suggest that T-type Ca channels could play a role in undifferentiated retinoblastoma cell physiology since alpha 1G and alpha 1H Ca channel subunit expression is reduced in cells that have differentiated and exited the cell cycle.
人视网膜母细胞瘤细胞是多能视网膜前体细胞，能够分化为光感受器、神经元和神经胶质细胞。未分化细胞的电流-电压关系主要由一种瞬时内向电流主导，该电流在分化后不久消失。在含有20 mM Ba(2+)的浴液中，该电流的激活中点接近-25 mV，并且在-20 mV时似乎完全失活。相对于Ba(2+)，Sr(2+)和Ca(2+)是更优的电荷载体，并且在没有这些二价阳离子的情况下电流消失。Cd(2+)以160 microM的半数抑制浓度（IC(50)）阻断电流，而Ni(2+)以双相方式阻断，IC(50)分别为22和352 microM。当用其他单价阳离子替代钠时，电流不受影响，并且它对硝苯地平、ω-芋螺毒素GVIA、ω-阿加毒素IVA和ω-芋螺毒素MVIIC不敏感。逆转录聚合酶链反应（RT-PCR）显示未分化细胞中存在α1G和α1H mRNA，但在分化后，发现α1G和α1H mRNA均显著减少，并且这与T型钙通道电流的丧失平行。在未分化和分化细胞中，α1I亚基mRNA水平较低。这些结果表明，T型钙通道可能在未分化的视网膜母细胞瘤细胞生理学中起作用，因为在已分化并退出细胞周期的细胞中，α1G和α1H钙通道亚基的表达减少。
