Akaike N, Lee K S, Brown A M
J Gen Physiol. 1978 May;71(5):509-31. doi: 10.1085/jgp.71.5.509.
Calcium current, Ica, was studied in isolated nerve cell bodies of Helix aspersa after suppression of Na+ and K+ currents. The suction pipette method described in the preceding paper was used. Ica rises to a peak value and then subsides exponentially and has a null potential of 150 mV or more and a relationship with [Ca2+]o that is hyperbolic over a small range of [Ca2+]o's. When [Ca2+]i is increased, Ica is reduced disproportionately, but the effect is not hyperbolic. Ica is blocked by extracellular Ni2+, La3+, Cd2+, and Co2+ and is greater when Ba2+ and Sr2+ carry the current. Saturation and blockage are described by a Langmuir adsorption relationship similar to that found in Balanus. Thus, the calcium conductance probably contains a site which binds the ions referred to. The site also appears to be voltage-dependent. Activation and inactivation of Ica are described by first order kinetics, and there is evidence that the processes are coupled. For example, inactivation is delayed slightly in its onset and tau inactivation depends upon the method of study. However, the currents are described equally well by either a noncoupled Hodgkin-Huxley mh scheme or a coupled reaction. Facilitation of Ica by prepulses was not observed. For times up to 50 ms, currents even at small depolarizations were accounted for by suitable adjustment of the activation and inactivation rate constants.
在抑制了Na⁺和K⁺电流后，对蛞蝓（Helix aspersa）分离的神经细胞体中的钙电流（Ica）进行了研究。采用了前文所述的吸移管法。Ica上升至峰值后呈指数下降，其零电位为150 mV或更高，并且在较小的[Ca²⁺]ₒ范围内与[Ca²⁺]ₒ呈双曲线关系。当[Ca²⁺]ᵢ增加时，Ica不成比例地降低，但这种效应并非双曲线关系。Ica被细胞外的Ni²⁺、La³⁺、Cd²⁺和Co²⁺阻断，当Ba²⁺和Sr²⁺携带电流时Ica更大。饱和与阻断可用类似于在藤壶（Balanus）中发现的朗缪尔吸附关系来描述。因此，钙电导可能包含一个与上述离子结合的位点。该位点似乎也依赖于电压。Ica的激活和失活可用一级动力学来描述，并且有证据表明这些过程是耦合的。例如，失活的起始稍有延迟，失活时间常数（tau inactivation）取决于研究方法。然而，电流用非耦合的霍奇金 - 赫胥黎（Hodgkin - Huxley）mh模型或耦合反应来描述效果同样良好。未观察到预脉冲对Ica的促进作用。在长达50 ms的时间内，即使是小的去极化电流也可通过适当调整激活和失活速率常数来解释。
