Hovav G, Parnas H, Parnas I
Department of Neurobiology, Hebrew University, Jerusalem, Israel.
Bull Math Biol. 1992 Sep;54(5):875-94. doi: 10.1007/BF02459934.
In order to account for the time courses of both evoked release and facilitation, in the framework of the Ca2+ hypothesis, Fogelson and Zucker (1985, Biophys. J. 48, 1003-1017) suggested treating diffusion of Ca2+, once it enters through the Ca2+ channels, as a three-dimensional process (three-dimensional diffusion model). This model is examined here as a refined version of the "Ca(2+)-theory" for neurotransmitter release. The three-dimensional model was suggested to account for both the time course of release and that of facilitation. As such, it has been examined here as to its ability to predict the dependence of the amplitude and time course of facilitation under various experimental conditions. It is demonstrated that the three-dimensional diffusion model predicts the time course of facilitation to be insensitive to temperature. It also predicts the amplitude and time course of facilitation to be independent of extracellular Ca2+ concentration. Moreover, it predicts that inhibition of the [Na+]o in equilibrium with [Ca2+]i exchange does not alter facilitation. These predictions are not upheld by the experimental results. Facilitation is prolonged upon reduction in temperature. The amplitude of facilitation declines and its duration is prolonged upon increase in extracellular Ca2+ concentration. Finally, inhibition of the [Na+]o in equilibrium with [Ca2+]i exchange prolongs facilitation but does not alter the time course of evoked release after an impulse.
为了解释诱发释放和易化作用的时间进程，在钙离子假说的框架下，福格尔森和朱克（1985年，《生物物理杂志》48卷，1003 - 1017页）建议，一旦钙离子通过钙离子通道进入，将其扩散视为一个三维过程（三维扩散模型）。在此，该模型作为神经递质释放的“钙离子理论”的一个改进版本进行检验。三维模型被认为可以解释释放和易化作用的时间进程。因此，在此检验了它在各种实验条件下预测易化作用的幅度和时间进程依赖性的能力。结果表明，三维扩散模型预测易化作用的时间进程对温度不敏感。它还预测易化作用的幅度和时间进程与细胞外钙离子浓度无关。此外，它预测抑制与细胞内钙离子交换平衡的细胞外钠离子浓度不会改变易化作用。这些预测与实验结果不符。降低温度会延长易化作用。增加细胞外钙离子浓度会使易化作用的幅度下降且持续时间延长。最后，抑制与细胞内钙离子交换平衡的细胞外钠离子浓度会延长易化作用，但不会改变冲动后诱发释放的时间进程。
