Kits K S, Mansvelder H D
Research Institute Neurosciences, Faculty of Biology, Vrije Universiteit, Amsterdam, Netherlands.
Invert Neurosci. 1996 Jun;2(1):9-34. doi: 10.1007/BF02336657.
Molluscan neurons and muscle cells express transient (T-type like) and sustained LVA calcium channels, as well as transient and sustained HVA channels. In addition weakly voltage sensitive calcium channels are observed. In a number of cases toxin or dihydropyridine sensitivity justifies classification of the HVA currents in L, N or P-type categories. In many cases, however, pharmacological characterization is still preliminary. Characterization of novel toxins from molluscivorous Conus snails may facilitate classification of molluscan calcium channels. Molluscan preparations have been very useful to study calcium dependent inactivation of calcium channels. Proposed mechanisms explain calcium dependent inactivation through direct interaction of Ca2+ with the channel, through dephosphorylation by calcium dependent phosphatases or through calcium dependent disruption of connections with the cytoskeleton. Transmitter modulation operating through various second messenger mediated pathways is well documented. In general, phosphorylation through PKA, cGMP dependent PK or PKC facilitates the calcium channels, while putative direct G-protein action inhibits the channels. Ca2+ and cGMP may inhibit the channels through activation of phosphodiesterases or phosphatases. Detailed evidence has been provided on the role of sustained LVA channels in pacemaking and the generation of firing patterns, and on the role of HVA channels in the dynamic changes in action potentials during spiking, the regulation of the release of transmitters and hormones, and the regulation of growth cone behavior and neurite outgrowth. The accessibility of molluscan preparations (e.g. the squid giant synapse for excitation release studies, Helisoma B5 neuron for neurite and synapse formation) and the large body of knowledge on electrophysiological properties and functional connections of identified molluscan neurons (e.g. sensory neurons, R15, egg laying hormone producing cells, etc.) creates valuable opportunities to increase the insight into the functional roles of calcium channels.
软体动物的神经元和肌肉细胞表达瞬时（类T型）和持续的低电压激活（LVA）钙通道，以及瞬时和持续的高电压激活（HVA）通道。此外，还观察到弱电压敏感性钙通道。在许多情况下，毒素或二氢吡啶敏感性可将HVA电流归类为L、N或P型。然而，在很多情况下，药理学特征描述仍处于初步阶段。对食软体动物的芋螺中新型毒素的表征可能有助于软体动物钙通道的分类。软体动物标本对于研究钙通道的钙依赖性失活非常有用。提出的机制解释了通过Ca2+与通道的直接相互作用、钙依赖性磷酸酶的去磷酸化或钙依赖性破坏与细胞骨架的连接来实现钙依赖性失活。通过各种第二信使介导途径进行的递质调节已有充分记录。一般来说，蛋白激酶A（PKA）、环鸟苷酸依赖性蛋白激酶或蛋白激酶C（PKC）介导的磷酸化促进钙通道，而假定的直接G蛋白作用则抑制通道。Ca2+和环鸟苷酸（cGMP）可能通过激活磷酸二酯酶或磷酸酶来抑制通道。已经提供了关于持续LVA通道在起搏和放电模式产生中的作用，以及HVA通道在动作电位爆发期间的动态变化、递质和激素释放的调节以及生长锥行为和神经突生长的调节中的作用的详细证据。软体动物标本的易获取性（例如用于兴奋释放研究的乌贼巨大突触、用于神经突和突触形成的黄斑海兔B5神经元）以及关于已鉴定的软体动物神经元（例如感觉神经元、R15、产卵激素产生细胞等）的电生理特性和功能连接的大量知识，为深入了解钙通道的功能作用创造了宝贵机会。
