KCNQ2 and KCNQ3 ion channel pore-forming subunits coassemble to form a heteromeric voltage-gated potassium channel that underlies the neuronal M-current. We and others showed that calmodulin (CaM) binds to specific sequence motifs in the C-terminal domain of KCNQ2 and KCNQ3. We also found that a fusion protein containing a KCNQ2 CaM-binding motif, coexpressed with KCNQ2 and KCNQ3, competes with the full-length KCNQ2 channel for CaM binding and thereby decreases KCNQ2/3 current density in heterologous cells. We have explored the importance of CaM binding for the generation of the native M-current and regulation of membrane excitability in rat hippocampal neurons in primary cell culture. M-current properties were studied in cultured neurons by using whole-cell patch clamp recording. The M-current density is lower in neurons expressing the CaM-binding motif fusion protein, as compared to control neurons transfected with vector alone. In contrast, no change in M-current density is observed in cells transfected with a mutant fusion protein that is unable to bind CaM. The CaM-binding fusion protein does not influence the rapidly inactivating A-current or the large conductance calcium-activated potassium channel-mediated fast spike afterhyperpolarization in neurons in which the M-current is suppressed. Furthermore, the CaM-binding fusion protein, but not the non-binding mutant, increases both the number of action potentials evoked by membrane depolarization and the size of the spike afterdepolarization. These results suggest that CaM binding regulates M-channel function and membrane excitability in the native neuronal environment.
|Number of pages
|Proceedings of the National Academy of Sciences of the United States of America
|Published - Nov 8 2005
ASJC Scopus subject areas