Abstract
HIGHLIGHTS - Calmodulin-dependent Kv7.2 current density without the need of binding calcium.- Kv7.2 current density increase is accompanied with resistance to PI(4,5)P(2) depletion.- Kv7.3 current density is insensitive to calmodulin elevation.- Kv7.3 is more sensitive to PI(4,5)P(2) depletion in the presence of calmodulin.- Apo-calmodulin influences PI(4,5)P(2) dependence in a subunit specific manner. The identification and understanding of critical factors regulating M-current functional density, whose main components are Kv7.2 and Kv7.3 subunits, has profound pathophysiological impact given the important role of the M-current in neuronal excitability control. We report the increase in current density of Kv7.2 channels by calmodulin (CaM) and by a mutant CaM unable to bind Ca(2+) (CaM(1234)) revealing that this potentiation is calcium independent. Furthermore, after co-expressing a CaM binding protein (CaM sponge) to reduce CaM cellular availability, Kv7.2 current density was reduced. Current inhibition after transient depletion of the essential Kv7 co-factor phosphatidylinositol-4,5-bisphosphate (PI(4,5)P(2)) by activating Danio rerio voltage sensitive phosphatase (DrVSP) was blunted by co-expressing CaM(1234) or the CaM sponge. In addition, CaM-dependent potentiation was occluded by tonic elevation of PI(4,5)P(2) levels by PI(4)P5-kinase (PIP5K) expression. In contrast to the effect on homomeric Kv7.2 channels, CaM(1234) failed to potentiate heteromeric Kv7.2/3 or homomeric Kv7.3 channels. Sensitivity to PI(4,5)P(2) depletion of Kv7.2/3 channels was increased after expression of CaM(1234) or the CaM sponge, while that of homomeric Kv7.3 was unaltered. Altogether, the data reveal that apo-CaM influences PI(4,5)P(2) dependence of Kv7.2, Kv7.2/3, and of Kv7.3 channels in a subunit specific manner.