Exploring GIRK Functionality in Human and Mouse Peripheral Neurons

Abstract

G protein coupled receptors (GPCRs) comprise over 17% of all approved drug targets, constituting the largest family of proteins targeted by currently available pharmaceutical treatments, including those for acute and chronic pain conditions. An important factor in inhibitory GPCR function is the activation of G protein-gated inwardly rectifying potassium (GIRK) channels. Upon activation GIRK channels hyperpolarize the cells and function as an important regulator of neuronal excitability. Selective targeting of these inhibitory GPCRs in peripheral neurons has garnered recent attention as this may help to reduce nociceptor activity that might avoid the negative side effects associated with these receptors in the central nervous system. The expression of various proteins differs greatly in the central nervous system from the periphery and much of our current knowledge on GIRK activation, and interplay with nociceptive circuits, is from the central nervous system. Here we asked whether activation of inhibitory GPCRs in peripheral sensory neurons couple to GIRK and voltage-gated Ca2+ channels to dampen excitability in human neurons. To investigate the availability of GIRKs we used RT-PCR to study the different GIRK subtypes expression in extracted whole DRG, from both human donors and C57BL/6J mice. To test for functional coupling, we used whole-cell patch clamp recordings in mouse and human neurons to directly study GIRK channel activation following treatment with several different families of Gi-coupled GPCR agonists. This allowed us to directly examine both the electrical and molecular components that might comprise peripheral GIRK channel activation, which adds new layers to the complexity of GPCR function in different neuron types. This study revealed previously unknown information about GIRK channels in both human and mouse DRG neurons. Going forward, the use of human DRG for preclinical molecular and functional studies may improve translational success in pharmaceutical treatments for numerous targets. Grant support from Gereau, R.W.: NS042595; The Dr. Seymour and Rose T. Brown Professorship in Anesthesiology Del Rosario, J: K00NS113422 Chamessian, A: American Neuromuscular Foundation Career Development Award Slivicki, R: F32DA051160-01.