Voltage-gated calcium channels (VGCCs) are a hallmark characteristic of excitable cells. Critical for regulating calcium levels within the cell, VGCCs are in-turn responsible for regulating numerous calcium-mediated biological processes including neurotransmitter release and gene transcription. For this reason, VGCCs are carefully modulated in healthy individuals, but in cases where there are alterations to the biophysical properties or the number of VGCCs, the effect on these fundamental pathways can lead to serious chronic disorders, and can be linked to cardiac, neurological and muscular diseases.
At the School of Pharmacy, University of Reading, we are investigating the modulation of these vital VGCCs with the view to developing therapeutic agents. Specifically, we are examining the action of signalling molecules (including novel brain proteins and G proteins) at sites and loops of the VGCC polypeptide chains that connect the transmembrane domains of this protein. (More information can be found in our book Modulation of Presynaptic Calcium Channels, G. Stephens and S. Mochida (eds.) Springer.)
With this aim, our recent work has led to the development of synthetic Ca2+ channel peptides. These synthetic peptides are based on CaV2.2 subunit intracellular amino-terminal and sites on the intracellular region connecting domains I and II (Bucci et al., 2011 J Physiology 589:3085-101). Importantly, these CaV2.2 peptides act as inhibitory modules, and decrease Ca2+ influx, potentially via direct effects on VGCC gating. Ultimately this leads to a reduction of synaptic transmission.
Interestingly, our research has shown that individual amino acid substitutions can generate CaV2.2 peptides with modified inhibitory effects. This suggests that we can use such peptides to further probe VGCC function and, potentially, form the basis for novel therapeutic development.
However, reliable delivery of therapeutic agents to intracellular sites of action is a significant barrier to the drug discovery process. Due to this problem, small hydrophilic molecules and, in particular, biological drugs such as peptides, often lack sufficient efficacy. At a basic bioscience level, improved intracellular delivery will have important impacts on elucidation of cell signalling pathways.
In our studies, our ~10-20mer peptides were injected into presynaptic terminals or cell soma of neurons via glass electrodes. In collaboration with Cellectricon, we now wish to use the Cellaxess Adherent Cell Electroporation platform to develop intracellular delivery of exogenously applied peptides. This may lead to the introduction of efficacious therapeutic agents based on these peptides (or small molecules that mirror their actions) in areas such as pharmacoresistant pain states.
Dr Gary Stephens holds the position of Reader in Pharmacology and is Director of Pharmacology & Therapeutics at the University of Reading School of Pharmacy. He is an in vitro electrophysiologist with research interests in ion channel and receptors, in particular, calcium channels and their role in synaptic transmission, as well as the modulation of these channels by novel signalling pathways.