Kv7 Channels Can Function without Constitutive Calmodulin Tethering

M-channels are voltage-gated potassium channels composed of Kv7.2-7.5 subunits that serve as important regulators of neuronal excitability. Calmodulin binding is required for Kv7 channel function and mutations in Kv7.2 that disrupt calmodulin binding cause Benign Familial Neonatal Convulsions (BFNC), a dominantly inherited human epilepsy. On the basis that Kv7.2 mutants deficient in calmodulin binding are not functional, calmodulin has been defined as an auxiliary subunit of Kv7 channels. However, we have identified a presumably phosphomimetic mutation S511D that permits calmodulin-independent function. Thus, our data reveal that constitutive tethering of calmodulin is not required for Kv7 channel function

Differential Regulation of PI(4,5)P2 Sensitivity of Kv7.2 and Kv7.3 Channels by Calmodulin.

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)P2 depletion.- Kv7.3 current density is insensitive to calmodulin elevation.- Kv7.3 is more sensitive to PI(4,5)P2 depletion in the presence of calmodulin.- Apo-calmodulin influences PI(4,5)P2 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 Ca2+ (CaM1234) 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)P2) by activating Danio rerio voltage sensitive phosphatase (DrVSP) was blunted by co-expressing CaM1234 or the CaM sponge. In addition, CaM-dependent potentiation was occluded by tonic elevation of PI(4,5)P2 levels by PI(4)P5-kinase (PIP5K) expression. In contrast to the effect on homomeric Kv7.2 channels, CaM1234 failed to potentiate heteromeric Kv7.2/3 or homomeric Kv7.3 channels. Sensitivity to PI(4,5)P2 depletion of Kv7.2/3 channels was increased after expression of CaM1234 or the CaM sponge, while that of homomeric Kv7.3 was unaltered. Altogether, the data reveal that apo-CaM influences PI(4,5)P2 dependence of Kv7.2, Kv7.2/3, and of Kv7.3 channels in a subunit specific manner.This work was supported by grants from the Spanish Ministry of Economy and Competitiveness (BFU2015-66910-R). CM. was funded by the Spanish Ministry of Economy and Competitiveness (PTA2012) and co-financed by the BERC program of the Basque Government. MT was an Ikerbasque Visiting Professor funded by the Basque Government, and work in MT laboratories was supported by Telethon (GGP15113).Peer reviewedPeer Reviewe

A pore residue of the KCNQ3 potassium M-channel subunit controls surface expression

KCNQ2 (Kv7.2) and KCNQ3 (Kv7.3) are the principal subunits underlying the potassium M-current, which exerts a strong control on neuronal excitability. KCNQ3 subunits coassemble with KCNQ2 to form functional heteromeric channels that are specifically transported to the axonal initial segment and nodes of Ranvier. In contrast, there is no evidence for functional homomeric KCNQ3 channels in neurons, and it appears that these are inefficiently trafficked to the plasma membrane. Among eukaryotic potassium channels, the KCNQ3 subunit is unusual because it has an alanine in place of a threonine at the pore inner vestibule, three residues upstream of the GYG signature sequence of the selectivity filter. This residue is critical for the potentiation of the current after heteromerization, but the mechanism is unknown. We report that the presence of this uncommon residue at position 315 has a strong impact on the stability of the homotetramers and on channel trafficking. Wild-type KCNQ3 expressed alone is retained within the endoplasmic reticulum, and this mechanism is overcome by the substitution of threonine for Ala315. KCNQ3 subunits require assembly with KCNQ2 to exit this compartment, whereas KCNQ3-A315T is no longer dependent on KCNQ2 to form channels that are efficiently trafficked to the plasma membrane. The presence of this alanine, therefore, plays an important role in regulating the subunit composition of functional M-channels expressed at the surface of neurons

Surface Expression and Subunit Specific Control of Steady Protein Levels by the Kv7.2 Helix A-B Linker

12 p.Kv7.2 and Kv7.3 are the main components of the neuronal voltage-dependent M-current, which is a subthreshold potassium conductance that exerts an important control on neuronal excitability. Despite their predominantly intracellular distribution, these channels must reach the plasma membrane in order to control neuronal activity. Thus, we analyzed the amino acid sequence of Kv7.2 to identify intrinsic signals that may control its surface expression. Removal of the interlinker connecting helix A and helix B of the intracellular C-terminus produces a large increase in the number of functional channels at the plasma membrane. Moreover, elimination of this linker increased the steady-state amount of protein, which was not associated with a decrease of protein degradation. The magnitude of this increase was inversely correlated with the number of helix A - helix B linkers present in the tetrameric channel assemblies. In contrast to the remarkable effect on the amount of Kv7.2 protein, removal of the Kv7.2 linker had no detectable impact on the steady-state levels of Kv7.3 protein.This work was supported by grants from the VII European framework program managed by the Fondo de Investigaciones Sanitarias (PI071316), from the Spanish Ministry of Education (BFU2009-07581 and SAF2006-1450), the Spanish Ion Channel Initiative Consolider project (CSD2008-00005), and the Basque Government (SAIOTEK SA-2006/00023). A. Alaimo was partially funded by Fundacion Biofisica Bizkaia. PA and JFO held a FPI fellowship from the Spanish Ministry of Science and Innovation (BES-2008-002314). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscrip

Effectiveness of a group intervention using pain neuroscience education and exercise in women with fibromyalgia: a pragmatic controlled study in primary care.

Very positive effects have been described in the application of pain neuroscience education (PNE) to chronic pain and migraine. However, there are few data on the applicability of this therapeutic approach in actual clinical practice in a primary care (PC) setting. The aim of this study was to explore the efficacy in fibromyalgia (FM) of an intervention based on PNE and exercise compared to treatment as usual (TAU). Pragmatic nonrandomised controlled trial set in 5 healthcare centres and one physiotherapy centre in PC. Fifty-three women with FM (2010 American College of Rheumatology Diagnostic Criteria for Fibromyalgia) were studied, 35 in the intervention group (IG) and 18 in the control group (CG). The women in the IG were interviewed individually and then received 6 weekly sessions plus one review session (1 month later): those in the CG received their TAU. The subject assignation to the CG or the IG was determined according to their availability to attend the sessions. They all filled in several questionnaires (prior to and 1 year after the intervention) to evaluate the impact of FM in their daily lives, catastrophism, anxiety and depression, severity and impact of pain in daily personal performance and functional capacity. The reductions (improvements) in the scores of all tests (baseline-final) were greater in the IG (p  An intervention based on PNE and exercise in patients with FM is feasible and seems effective in PC. The study was retrospectively registered at ClinicalTrials.gov (Trial Registration NCT04539171 ), on 04/09/2020