Straiker Alex, Sullivan Jane M
The Salk Institute and the University of California, San Diego, La Jolla 92037, USA.
J Neurophysiol. 2003 May;89(5):2647-54. doi: 10.1152/jn.00268.2002.
Cannabinoid CB1 receptors have been detected in retinas of numerous species, with prominent labeling in photoreceptor terminals of the chick and monkey. CB1 labeling is well-conserved across species, suggesting that CB1 receptors might also be present in photoreceptors of the tiger salamander. Synaptic transmission in vertebrate photoreceptors is mediated by L-type calcium currents-currents that are modulated by CB1 receptors in bipolar cells of the tiger salamander. Presence of CB1 receptors in photoreceptor terminals would therefore be consistent with presynaptic modulation of synaptic transmission, a role seen for cannabinoids in other parts of the brain. Here we report immunohistochemical and electrophysiological evidence for the presence of functional CB1 receptors in rod and cone photoreceptors of the tiger salamander. The cannabinoid receptor agonist WIN 55212-2 enhances calcium currents of rod photoreceptors by 39% but decreases calcium currents of large single cones by 50%. In addition, WIN 55212-2 suppresses potassium currents of rods and large single cones by 44 and 48%, respectively. Thus functional CB1 receptors, present in the terminals of rod and cone photoreceptors, differentially modulate calcium and potassium currents in rods and large single cones. CB1 receptors are therefore well positioned to modulate neurotransmitter release at the first synapse of the visual system.
在许多物种的视网膜中都检测到了大麻素CB1受体，在鸡和猴子的光感受器终末有明显的标记。CB1标记在不同物种间高度保守，这表明CB1受体可能也存在于虎螈的光感受器中。脊椎动物光感受器中的突触传递由L型钙电流介导，而在虎螈双极细胞中，这些电流受CB1受体调节。因此，光感受器终末存在CB1受体与突触传递的突触前调制是一致的，大麻素在大脑其他部位也发挥着这种作用。在此，我们报告了虎螈视杆和视锥光感受器中存在功能性CB1受体的免疫组织化学和电生理学证据。大麻素受体激动剂WIN 55212-2可使视杆光感受器的钙电流增强39%，但使大的单视锥细胞的钙电流降低50%。此外，WIN 55212-2分别使视杆和大的单视锥细胞的钾电流抑制44%和48%。因此，存在于视杆和视锥光感受器终末的功能性CB1受体，对视杆和大的单视锥细胞中的钙电流和钾电流有不同的调节作用。因此，CB1受体能够很好地调节视觉系统第一个突触处的神经递质释放。
