FULL-LENGTH AND TRUNCATED KV1.3 K+ CHANNELS ARE MODULATED BY 5-HT(1C) RECEPTOR ACTIVATION AND INDEPENDENTLY BY PKC

In T-cells, the Shaker-related gene, Kv1.3 encodes the type n K+ channel, whereas the type l channel is a product of the Shaw subfamily gene, Kv3.1. Both these genes are also expressed in the brain. We have used the Xenopus oocyte heterologous expression system to study the modulatory effects of serotonin (5-hydroxytryptamine, 5-HT) on both these cloned channels. In oocytes coexpressing the mouse 5-HT1c receptor and mouse Kv1.3 channel, addition of 100 nM 5-HT causes a complete and sustained suppression of Kv1.3 currents in approximately 20 min. In contrast, 5-HT has no effect on mouse Kv3.1 currents when coexpressed with 5-HT1c receptor. The 5-HT-mediated suppression of Kv1.3 currents proceeds via activation of a pertussis toxin-sensitive G protein and a subsequent rise in intracellular Ca2+, but Ca2+ does not directly block the channel. Protein kinase (PK) C activation is not part of the pathway linking 5-HT1c receptor to Kv1.3 channels. However, phorbol esters independently suppress Kv1.3 currents. Deletion of the first 146 amino acids from the NH2-terminal, containing putative tyrosine kinase and PKA phosphorylation sites, does not alter the time course of 5-HT-mediated suppression of Kv1.3 currents, indicating that these residues are not necessary for modulation. Treatment of oocytes with calmodulin or phosphatase inhibitors does not alter 5-HT-mediated modulation. Collectively, these experiments indicate that the mouse Kv1.3 channel is capable of being modulated by 5-HT via 5-HT1c receptor in a G protein and Ca2+-dependent manner, but the subsequent steps in the pathway remain elusive. PKC also suppresses Kv1.3 currents but by an independent pathway.