A Comprehensive Integrated Anatomical and Molecular Atlas of Rat Intrinsic Cardiac Nervous System.

We have developed and integrated several technologies including whole-organ imaging and software development to support an initial precise 3D neuroanatomical mapping and molecular phenotyping of the intracardiac nervous system (ICN). While qualitative and gross anatomical descriptions of the anatomy of the ICN have each been pursued, we here bring forth a comprehensive atlas of the entire rat ICN at single-cell resolution. Our work precisely integrates anatomical and molecular data in the 3D digitally reconstructed whole heart with resolution at the micron scale. We now display the full extent and the position of neuronal clusters on the base and posterior left atrium of the rat heart, and the distribution of molecular phenotypes that are defined along the base-to-apex axis, which had not been previously described. The development of these approaches needed for this work has produced method pipelines that provide the means for mapping other organs.

A novel selective and orally bioavailable Nav 1.8 channel blocker, PF-01247324, attenuates nociception and sensory neuron excitability.

BACKGROUND AND PURPOSE: NaV 1.8 ion channels have been highlighted as important molecular targets for the design of low MW blockers for the treatment of chronic pain. Here, we describe the effects of PF-01247324, a new generation, selective, orally bioavailable Nav 1.8 channel blocker of novel chemotype. EXPERIMENTAL APPROACH: The inhibition of Nav 1.8 channels by PF-01247324 was studied using in vitro patch-clamp electrophysiology and the oral bioavailability and antinociceptive effects demonstrated using in vivo rodent models of inflammatory and neuropathic pain. KEY RESULTS: PF-01247324 inhibited native tetrodotoxin-resistant (TTX-R) currents in human dorsal root ganglion (DRG) neurons (IC50 : 331 nM) and in recombinantly expressed h Nav 1.8 channels (IC50 : 196 nM), with 50-fold selectivity over recombinantly expressed TTX-R hNav 1.5 channels (IC50 : ∼10 µM) and 65-100-fold selectivity over TTX-sensitive (TTX-S) channels (IC50 : ∼10-18 µM). Native TTX-R currents in small-diameter rodent DRG neurons were inhibited with an IC50 448 nM, and the block of both human recombinant Nav 1.8 channels and TTX-R from rat DRG neurons was both frequency and state dependent. In vitro current clamp showed that PF-01247324 reduced excitability in both rat and human DRG neurons and also altered the waveform of the action potential. In vivo experiments n rodents demonstrated efficacy in both inflammatory and neuropathic pain models. CONCLUSIONS AND IMPLICATIONS: Using PF-01247324, we have confirmed a role for Nav 1.8 channels in both inflammatory and neuropathic pain. We have also demonstrated a key role for Nav 1.8 channels in action potential upstroke and repetitive firing of rat and human DRG neurons.

Isoform-selective voltage-gated Na(+) channel modulators as next-generation analgesics.

For many patients the current therapies for controlling chronic pain are inadequate. This has driven the search for analgesics with improved efficacy and side effect profiles. Some anticonvulsants have voltage-gated Na(+) channels (VGSCs) as their molecular targets and are used to treat pain, but the efficacy seen is marginal and the drugs are generally poorly tolerated. The clinically used VGSC-modulating analgesics show no isoform selectivity, which probably limits their use. Thus, focus has fallen on VGSCs expressed selectively by primary afferent neurons and the search for isoform-selective drugs. In this review, we describe developments in our understanding of the biology of VGSCs, screening technologies and the pharmacological properties of VGSC modulators with promise as analgesics. Also highlighted are the challenges associated with targeting isoform-selective VGSCs.

Subtype-selective targeting of voltage-gated sodium channels.

Voltage-gated sodium channels are key to the initiation and propagation of action potentials in electrically excitable cells. Molecular characterization has shown there to be nine functional members of the family, with a high degree of sequence homology between the channels. This homology translates into similar biophysical and pharmacological properties. Confidence in some of the channels as drug targets has been boosted by the discovery of human mutations in the genes encoding a number of them, which give rise to clinical conditions commensurate with the changes predicted from the altered channel biophysics. As a result, they have received much attention for their therapeutic potential. Sodium channels represent well-precedented drug targets as antidysrhythmics, anticonvulsants and local anaesthetics provide good clinical efficacy, driven through pharmacology at these channels. However, electrophysiological characterization of clinically useful compounds in recombinant expression systems shows them to be weak, with poor selectivity between channel types. This has led to the search for subtype-selective modulators, which offer the promise of treatments with improved clinical efficacy and better toleration. Despite developments in high-throughput electrophysiology platforms, this has proven very challenging. Structural biology is beginning to offer us a greater understanding of the three-dimensional structure of voltage-gated ion channels, bringing with it the opportunity to do real structure-based drug design in the future. This discipline is still in its infancy, but developments with the expression and purification of prokaryotic sodium channels offer the promise of structure-based drug design in the not too distant future.

Voltage-gated sodium channels: the search for subtype-selective analgesics.

BACKGROUND: Primary afferent or sensory neurons innervate almost all the tissues of the body. They are vital in receiving sensory information and conveying this to the spinal cord and subsequently to the brain, where the higher centres convert this afferent input into an 'understanding' of its nature. The nociceptors are a subset of sensory neurons responsible for the transmission of 'painful' stimuli into the CNS. OBJECTIVE/METHODS: Voltage-gated sodium channels (VGSCs) are pivotal in the transduction of noxious signals at the terminals of the nociceptors and the transmission of the signal along the axon and into the spinal cord and brain. There are nine functional members of the VGSC family. This review aims to briefly summarise the biology of the family, discuss those VGSCs involved in the transduction and transmission of nociceptive signals and to highlight the potential and also the challenges in seeking subtype-selective VGSC modulators for the effective treatment of pain. RESULTS/CONCLUSION: Robust evidence from preclinical models - and better yet, overwhelming human clinical genetic data - provides a compelling rationale for the involvement of VGSCs in nociceptive processing. Some compounds showing a low degree of subtype selectivity have been progressed into clinical development, but the results have been disappointing. It is likely that the high degree of structural homology within the VGSC family is a causative factor in making the discovery of subtype-selective modulators extremely challenging. A much greater understanding of the structure - function relationship for VGSCs and pharmacological modulators is needed if we are to design the compounds that will target those channels involved in nociceptive signalling whilst sparing those in the heart and brain. Only then will we be able to deliver a quantum leap in analgesic pharmacotherapy, providing the effective and well-tolerated drugs that the patient needs.