The inward rectifier family of potassium (Kir) channels is comprised of at least 16 family members exhibiting broad and often overlapping cellular, tissue, or organ distributions. The discovery of disease-causing mutations in humans and experiments on knockout mice has underscored the importance of Kir channels in physiology and in some cases raised questions about their potential as drug targets. However, the paucity of potent and selective small-molecule modulators targeting specific family members has with few exceptions mired efforts to understand their physiology and assess their therapeutic potential. A growing body of evidence suggests that G protein-coupled inward rectifier K (GIRK) channels of the Kir3.X subfamily may represent novel targets for the treatment of atrial fibrillation. In an effort to expand the molecular pharmacology of GIRK, we performed a thallium (Tl+) flux-based high-throughput screen of a Kir1.1 inhibitor library for modulators of GIRK. One compound, termed VU573, exhibited 10-fold selectivity for GIRK over Kir1.1 (IC50 = 1.9 and 19 μM, respectively) and was therefore selected for further study. In electrophysiological experiments performed on Xenopus laevis oocytes and mammalian cells, VU573 inhibited Kir3.1/3.2 (neuronal GIRK) and Kir3.1/3.4 (cardiac GIRK) channels with equal potency and preferentially inhibited GIRK, Kir2.3, and Kir7.1 over Kir1.1 and Kir2.1.Tl+ flux assays were established for Kir2.3 and the M125R pore mutant of Kir7.1 to support medicinal chemistry efforts to develop more potent and selective analogs for these channels. The structure–activity relationships of VU573 revealed few analogs with improved potency, however two compounds retained most of their activity toward GIRK and Kir2.3 and lost activity toward Kir7.1. We anticipate that the VU573 series will be useful for exploring the physiology and structure–function relationships of these Kir channels.

Inward rectifier potassium (Kir) channels have been postulated as therapeutic targets for several common disorders including hypertension, cardiac arrhythmias and pain. With few exceptions, however, the small-molecule pharmacology of this family is limited to nonselective cardiovascular and neurologic drugs with off-target activity toward inward rectifiers. Consequently, the actual therapeutic potential and 'drugability' of most Kir channels has not yet been determined experimentally. The purpose of this review is to provide a comprehensive summary of publicly disclosed Kir channel small-molecule modulators and highlight recent targeted drug-discovery efforts toward Kir1.1 and Kir2.1. The review concludes with a brief speculation on how the field of Kir channel pharmacology will develop over the coming years and a discussion of the increasingly important role academic laboratories will play in this progress.Members of the inward rectifier family of potassium (Kir) channels regulate a myriad of physiological processes, including cardiac function, pain processing and opioid action, learning and memory, insulin secretion and epithelial solute transport [1,2]. Some inward rectifiers occupy unique physiological niches that raise intriguing questions about their potential as therapeutic targets. Unfortunately, however, the small-molecule pharmacology of inward rectifiers has remained essentially undeveloped since the first member was cloned nearly 20 years ago [3]. This dearth of pharmacological tools has hindered efforts to develop even a cursory understanding of the physiology of some Kir channels and represents a critical barrier to defining their therapeutic potential. The main goals of this review article are:• To provide a comprehensive summary of disclosed small-molecule modulators of Kir channels, highlighting the few examples where pharmacology has illuminated a deeper understanding of their physiology and 'druggability'; © 2010 Future Science Ltd † Author for correspondence: Tel.: +1 615 343 7385, Fax: +1 615 343 3916, jerod.s.denton@vanderbilt.edu. Financial & competing interests disclosureThe authors are supported by NIH grants 1R21NS5704111 (Jerod S Denton) and 1U54MH084659-01 (Brian A Chauder), an American Heart Association-Southeast Affiliate Beginning Grant-In-Aid (Jerod S Denton), a National Kidney Foundation Postdoctoral Fellowhip grant (Gautam Bhave) and the Vanderbilt Department of Anesthesiology BH Robbins Scholars Program (Daniel Lonergan).The authors have no other relevant affliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.No writing assistance was utilized in the production of this manuscript. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript• To review recent adva...

Summary Variations in the KCNJ6 gene appear to influence both acute and chronic pain phenotypes. G-protein coupled inwardly rectifying potassium (GIRK) channels are effectors determining degree of analgesia experienced upon opioid receptor activation by endogenous and exogenous opioids. The impact of GIRK-related genetic variation on human pain responses has received little research attention. We used a tag SNP approach to comprehensively examine pain-related effects of KCNJ3 (GIRK1) and KCNJ6 (GIRK2) gene variation. Forty-one KCNJ3 and 69 KCNJ6 tag SNPs were selected, capturing the known variability in each gene. The primary sample included 311 Caucasian patients undergoing total knee arthroplasty in whom post-surgical oral opioid analgesic medication order data were available. Primary sample findings were then replicated in an independent Caucasian sample of 63 healthy pain-free individuals and 75 individuals with chronic low back pain (CLBP) who provided data regarding laboratory acute pain responsiveness (ischemic task) and chronic pain intensity and unpleasantness (CLBP Only). Univariate quantitative trait analyses in the primary sample revealed that 8 KCNJ6 SNPs were significantly associated with the medication order phenotype (p < 0.05); overall effects of the KCNJ6 gene (gene set-based analysis) just failed to reach significance (p=.054). No significant KCNJ3 effects were observed. A continuous GIRK Related Risk Score (GRRS) was derived in the primary sample to summarize each individual's number of KCNJ6 “pain risk” alleles. This GRRS was applied to the replication sample, which revealed significant associations (p<.05) between higher GRRS values and lower acute pain tolerance and higher CLBP intensity and unpleasantness. Results suggest further exploration of the impact of KCNJ6 genetic variation on pain outcomes is warranted.

This preliminary work demonstrates the safety of abrupt IT opioid cessation utilizing standardized inpatient withdrawal protocols. To our knowledge, these are among the first reported cases of intentional, controlled IT opioid cessation without initiation of an opioid bridge: self-reported pain scores, functional capacity, and quality of life improved. The IT opioid withdrawal syndrome is characterized based upon our observations and a review of the literature.

Patients who struggle with both pain and addiction present with some of the most challenging scenarios in clinical medicine. An understanding of the neurophysiologic basis of addiction is a key element in the proper management of acute and chronic pain. Physicians should appropriately screen for addiction and employ a comprehensive and safe approach to pain management, especially for patients with risk factors or a history significant for opioid addiction. Physicians should also understand the legal and regulatory issues governing the prescribing and dispensing of controlled substances in the course of treatment for acute pain, chronic pain, and addiction.