Co-expression of the voltage-gated potassium channel Kv1.4 with transient receptor potential channels (TRPV1 and TRPV2) and the cannabinoid receptor CB1 in rat dorsal root ganglion neurons

Potassium channels contribute to basic neuronal excitability and modulation. Here, we examined expression patterns of the voltage-gated potassium channel Kv1.4, the nociceptive transduction channels TRPV1 and TRPV2 as well as the putative anti-nociceptive cannabinoid receptor CB1 by immunofluorescence double-labelings in sections of rat dorsal root ganglia (DRGs).Kv1.4, TRPV1 and CB1 were each detected in about one third of neurons (35.7±0.5%, 29.4±1.1% and 36.4±0.5%, respectively, mean diameter 19.1±0.3 μm). TRPV2 was present in 4.4±0.4% of all neurons that were significantly larger in diameter (27.4±0.7 μm; P<0.001). Antibody double-labeling revealed that the majority of Kv1.4-positive neurons co-expressed TRPV1 (73.9±1.5%) whereas none expressed TRPV2. The largest overlap was found with CB1 (93.1±0.1%). CB1 expression resembled that seen for Kv1.4 since the majority of neurons expressing CB1-protein also expressed TRPV1 (69.4±6.5%) but not TRPV2 (0.6±0.3%). When CB1-mRNA was detected using in situ hybridizations an additional subset of larger neurons was labeled including 82.4±17.7% of the TRPV2 expressing neurons. However, co-localization of Kv1.4 with CB1-mRNA (92%, mean diameter: 18.5 μm) was essentially the same as with CB1-protein.The almost complete overlap of CB1 and Kv1.4 in nociceptive DRG neurons suggests a functional synergistic action between Kv1.4 and CB1. The potassium channel may have two important roles in nociception. As the molecular basis of A-type current it could be involved in the control of repetitive discharges at peripheral terminals and as a downstream signal transduction site of CB1 in the control of presynaptic transmitter release at central terminals.