Cholesterol increases the open probability of cardiac KACh currents.

Cholesterol is one of the major lipid components of membranes in mammalian cells. In recent years, cholesterol has emerged as a major regulator of ion channel function. The most common effect of cholesterol on ion channels in general and on inwardly rectifying potassium (Kir) channels in particular is a decrease in activity. In contrast, we have recently shown that native G-protein gated Kir (GIRK or Kir3) channels that underlie atrial KACh currents are up-regulated by cholesterol. Here we unveil the biophysical basis of cholesterol-induced increase in KACh activity. Using planar lipid bilayers we show that cholesterol significantly enhances the channel open frequency of the Kir3.1/Kir3.4 channels, which underlie KACh currents. In contrast, our data indicate that cholesterol does not affect their unitary conductance. Furthermore, using fluorescent and TIRF microscopy as well as surface protein biotinylation, we also show that cholesterol enrichment in vitro has no effect on surface expression of GFP-tagged channels expressed in Xenopus oocytes or transfected into HEK293 cells. Together, these data demonstrate for the first time that cholesterol enhances Kir3-mediated current by increasing the channel open probability.

Distant cytosolic residues mediate a two-way molecular switch that controls the modulation of inwardly rectifying potassium (Kir) channels by cholesterol and phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)).

BACKGROUND: Cholesterol modulates inwardly rectifying potassium (Kir) channels. RESULTS: A two-way molecular cytosolic switch controls channel modulation by cholesterol and PI(4,5)P(2). CONCLUSION: Cholesterol and PI(4,5)P(2) induce a common gating pathway of Kir2.1 despite their opposite impact on channel function. SIGNIFICANCE: These findings provide insights into structure-function relationship of ion channels and contribute to understanding of the mechanisms underlying their regulation by lipids. Inwardly rectifying potassium (Kir) channels play an important role in setting the resting membrane potential and modulating membrane excitability. An emerging feature of several Kir channels is that they are regulated by cholesterol. However, the mechanism by which cholesterol affects channel function is unclear. Here we show that mutations of two distant Kir2.1 cytosolic residues, Leu-222 and Asn-251, form a two-way molecular switch that controls channel modulation by cholesterol and affects critical hydrogen bonding. Notably, these two residues are linked by a residue chain that continues from Asn-251 to connect adjacent subunits. Furthermore, our data indicate that the same switch also regulates the sensitivity of the channels to phosphatidylinositol 4,5-bisphosphate, a phosphoinositide that is required for activation of Kir channels. Thus, although cholesterol and phosphatidylinositol 4,5-bisphosphate do not interact with the same region of Kir2.1, these different modulators induce a common gating pathway of the channel.

Efficacy of Targeted Mast Cell Inhibition Therapy in Chronic Prostatitis/Chronic Pelvic Pain Syndrome.

OBJECTIVE: To identify a subgroup of patients with mast cell dysfunction in chronic prostatitis/chronic pelvic pain syndrome and evaluate efficacy of mast cell-directed therapy. MATERIALS AND METHODS: Men with chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) were recruited and evaluated in an open-label, interventional uncontrolled trial after therapy with cromolyn sodium and cetirizine hydrochloride. The primary endpoint was a change in mast cell tryptase concentrations after treatment while secondary endpoints were changes in the National Institutes of Health Chronic Prostatitis Symptom Index (NIH-CPSI) and AUA-SI. Isolated cells from postprostatic massage urine were evaluated for immune changes using mRNA expression analysis. RESULTS: 31 patients with a diagnoses of Category III CP/CPPS were consented, 25 patients qualified and 20 completed the study after meeting a prespecified threshold for active tryptase in expressed prostatic secretions. After treatment with cromolyn sodium and cetirizine dihydrochloride for 3-week, active tryptase concentrations were significantly reduced from 49.03±14.05 ug/mL to 25.49±5.48 ug/mL (P<.05). The NIH-CPSI total score was reduced with a mean difference of 5.2±1 along with reduction in the pain, urinary and quality of life subscores (P<.001). A reduction in the AUA-SI was observed following treatment (P<.05). NanoString mRNA analysis of isolated cells revealed downregulation of immune-related pathways including Th1 and Th17 T cell differentiation and TLR signaling. Marked reduction in CD45+ cells and specifically macrophages and neutrophil abundance was observed. CONCLUSION: Identification of CP/CPPS patients with mast cell dysfunction may be achieved using tryptase as a discriminating biomarker. Mast cell-directed therapy in this targeted subgroup may be effective in reducing symptoms and modulating the immune inflammatory environment.

The atypical dopamine D1 receptor agonist SKF 83959 induces striatal Fos expression in rats.

The effects of dopamine D1 receptor agonists are often presumed to result from an activation of adenylyl cyclase, but dopamine D1 receptors may also be linked to other signal transduction cascades and the relative importance of these various pathways is currently unclear. SKF 83959 is an agonist at dopamine D1 receptors linked to phospholipase C, but has been reported to be an antagonist at receptors linked to adenylyl cyclase. The current report demonstrates that SKF 83959 induces pronounced, nonpatchy, expression of the immediate-early gene product Fos in the striatum of intact rats which can be converted to a patchy pattern by pretreatment with the dopamine D2-like receptor agonist quinpirole. In rats with unilateral 6-hydroxydopamine lesions SKF 83959 induces strong behavioral rotation and a greatly potentiated Fos response. All of the responses to SKF 83959, in both intact and dopamine-depleted animals, can be blocked by pretreatment with the dopamine D1 receptor antagonist SCH-23390. In intact subjects, SKF 83959 induced Fos expression less potently than the standard dopamine D1 receptor agonist SKF 82958, but the two drugs were approximately equipotent in deinnervated animals. These results demonstrate for the first time that possession of full efficacy at dopamine D1 receptors linked to adenylyl cyclase is not a necessary requirement for the induction of striatal Fos expression in intact animals and suggest that alternative signal transduction pathways may play a role in dopamine agonist induced Fos expression, especially in dopamine-depleted subjects.

The distribution of m4 muscarinic acetylcholine receptors in the islands of Calleja and striatum of rats and cynomolgus monkeys.

The distribution of m4 muscarinic acetylcholine receptors, and their relation to a number other markers, was examined using immunocytochemical techniques. Staining in the dorsal striatum tended to be more pronounced in the striosomal than the matrix compartment of both rats and cynomolgus monkeys. Within the ventral striatum, immunoreactivity was more pronounced within the olfactory tubercle and the shell region of the nucleus accumbens than in the nucleus accumbens core and was especially marked within the lateral striatal stripe. Modest staining was also seen in the external plexiform layer of the olfactory bulb. By far, the most intense staining in the forebrain of both rats and cynomolgus monkeys was found in islands of Calleja, where it appeared to be a selective marker for the core or hilus regions of the islands, or an analogous region found adjacent to them. The core regions of different islands appear to be continuous with each other so as to form a complex three-dimensional structure, which is largely encased by layers of granule cells. The neuronal elements in the islands of Calleja, which express m4 receptors, remain to be identified, but it is unlikely that cholinergic neurons are a major locus of these receptors. Although there are certain similarities between the islands of Calleja and other components of the striatal complex, the current studies emphasize the extent to which the islands are unique in terms of their architecture and chemical anatomy.