Cannabinoid Receptor Activation Differentially Modulates Ion Channels in Photoreceptors of the Tiger Salamander

May 13, 2003Journal of neurophysiology

Cannabinoid receptor activation differently affects ion channels in tiger salamander light-sensing cells

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Abstract

Functional cannabinoid CB1 receptors in rod and cone photoreceptors of the tiger salamander were identified, affecting calcium and potassium currents.

CB1 receptors were detected in both rod and cone photoreceptors of the tiger salamander.
The cannabinoid receptor agonist WIN 55212-2 increased calcium currents in rod photoreceptors by 39%, while it decreased calcium currents in large single cones by 50%.
WIN 55212-2 also suppressed potassium currents in rods and large single cones by 44% and 48%, respectively.
These findings suggest that CB1 receptors may differentially influence synaptic transmission in the visual system.

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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.

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Cannabinoid Receptor Activation Differentially Modulates Ion Channels in Photoreceptors of the Tiger Salamander

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