By controlling the flow of potassium ions, K+-channels play key roles in processes such as cell differentiation, immune responses, excitability, cell death, etc. The importance of these channels is further emphasised by the fact that they are present in virtually every cell of the body. More than 75 human genes encode K+-channel subunits and by combining different subunits, a huge variety of K+ channels can be generated.

The fact that defects in these proteins can produce disorders is itself very striking given the potential degree of K+ channel redundancy, highlighting that the "why, where, when and how" of potassium currents is very important. Indeed, the fact that some K+-channels cannot be replaced by others indicates that they fulfil very special needs.

So far, about ten potassium channelopathies are known and in this respect, the KCNQ family (Kv7) is remarkable since mutations in four of the five KCNQ channels are responsible for pathological disorders. Mutations in KCNQ2 and KCNQ3 cause neonatal convulsions (BFNC), whereas in KCNQ4 they cause progressive hearing loss. Furthermore, mutations in the non-neuronal KCNQ1, cause cardiac arrhythmia (LQT1 syndrome), and when homozygous this channel also produce deafness.

Thus, potassium flow through the KCNQ family of proteins is crucial for the correct functioning of the cell.

The M-current was so named as it was suppressed by the action of acetylcholine on muscarinic receptors. When the KCNQ2 and KCNQ3 genes were shown to be involved in BFNC, it was discovered that the current they produced was indistinguishable from the M-current. Subsequently, the KCNQ4 and KCNQ5 subunits were isolated, adding to the diversity of M-channels.

In hippocampal pyramidal neurons, KCNQ2/3 heteromultimers form the principal component of the M-current. However, in some neurons KCNQ3/5 heteromultimers or KCNQ5 homomers may contribute a further component. This suggests that KCNQ5 may well be involved in other unidentified pathological disorders, although their nature is difficult to predict.

Benign Familial Neonatal Convulsions (BFNC) is a rare autosomal-dominant disorder that is caused by mutations in the KCNQ2 and KCNQ3. The variety of conditions that are associated with BNFC suggests a broader than expected role of KCNQ channels in neuronal pathophysiology. Thus, one of the principal aims of this project will be to understand the cellular biological basis underlying this and the associated pathological conditions.

The precise cellular localisation of ion channels influences the electrical properties of neurons. Indeed, KCNQ channels are not homogeneously distributed at the surface of hippocampal neurons but rather interactions between channels, scaffolding proteins, and the cytoskeleton control the spatial organisation of channels. In addition other mechanisms may control subcellular localisation, such as selective retention, endocytosis and intracellular trafficking.

Each KCNQ subunits contain six transmembrane segments, with the N- and C-terminal segments in the cell interior. Analysis of the C-terminal region reveals the existence of four helices that mediate the interactions between the channels and accessory proteins and that determine the specificity of subunit assembly. Moreover, although the details underlying cellular trafficking and targeting are unclear, the C-terminal region is important for efficient surface expression.

The regulation of the M-current by neurotransmitters is complex and poorly understood, and the intracellular second messengers involved have remained elusive for decades. While G-proteins mediate the effects, there is evidence that a diffusible second messenger are at play, and there are indications of a complex interaction of intracellular Ca2+, PIP2, PKC and other mediators. One aim is to clarify the relation among the different pathways that modulate the M-current.

KCNQ channelopathies provide an example of the importance of gene dosage in inherited disease. Disease-causing missense mutations in BFNC are associated with only a modest reduction (20-30%) in current magnitude. Thus, mutations that only moderately reduce channel expression may be pathological. Indeed, despite the fact that the coding region and splice junctions of KCNQ2 have been extensively probed for mutations that cause BFNC, in many patients the genetic alteration remains unidentified, and may lie outside the coding region. For this reason, we will study how the expression of these genes is regulated.

The action of acetylcholine is particularly important in cognition and the M-current is one of its targets. Certain cognition enhancing drugs increase acetylcholine release and act on M-channels. Furthermore, the effects of such drugs on LTP suggest that the M-current may be important for learning and memory. Hence, we will dedicate some effort towards defining the involvement of the M-current in neuronal plasticity.

The recent discovery that a new anticonvulsant drug is capable of opening KCNQ channels in neuronal cells is of great interest given that more than 25% of patients with generalised epilepsy do not receive satisfactory pharmacological treatment. There is also some evidence that modulating KCNQ channel activity may also have a therapeutic impact on neurodegenerative diseases and for the treatment of pain. It is important for us to understand more precisely how the available modulators of KCNQ channels work, since this may help in developing more selective drugs.

The KCNQ4 gene is responsible for a congenital profound loss of hearing. KCNQ4 is prominently expressed in the inner ear and in many nuclei tracts of the central auditory pathway in the brainstem. By further studying the contribution of M-channels to the auditory pathway we hope to obtain important insights into deafness and possibly create the basis for novel therapies.