PKD2, or polycystin 2, the product of the gene mutated in type 2 autosomal dominant polycystic kidney disease, belongs to the transient receptor potential channel superfamily and has been shown to function as a nonselective cation channel in the plasma membrane. However, the mechanism of PKD2 activation remains elusive. We show that PKD2 overexpression increases epidermal growth factor (EGF)-induced inward currents in LLC-PK1 kidney epithelial cells, while the knockdown of endogenous PKD2 by RNA interference or the expression of a pathogenic missense variant, PKD2-D511V, blunts the EGF-induced response. Pharmacological experiments indicate that the EGF-induced activation of PKD2 occurs independently of store depletion but requires the activity of phospholipase C (PLC) and phosphoinositide 3-kinase (PI3K). Pipette infusion of purified phosphatidylinositol-4,5-bisphosphate (PIP2) suppresses the PKD2-mediated effect on EGF-induced conductance, while pipette infusion of phosphatidylinositol-3,4,5-trisphosphate (PIP3) does not have any effect on this conductance. Overexpression of type Iα phosphatidylinositol-4-phosphate 5-kinase [PIP(5)Kα], which catalyzes the formation of PIP2, suppresses EGF-induced currents. Biochemical experiments show that PKD2 physically interacts with PLC-γ2 and EGF receptor (EGFR) in transfected HEK293T cells and colocalizes with EGFR and PIP2 in the primary cilium of LLC-PK1 cells. We propose that plasma membrane PKD2 is under negative regulation by PIP2. EGF may reduce the threshold of PKD2 activation by mechanical and other stimuli by releasing it from PIP2-mediated inhibition.

Clinical studies reveal concomitant occurrence of several gastrointestinal and urologic disorders, including irritable bowel syndrome and interstitial cystitis. The purpose of this study was to determine the mechanisms underlying cross-organ sensitization at the level of dorsal root ganglion (DRG) after acute and subsided gastrointestinal inflammation. DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate) and Fast Blue were injected into the distal colon and urinary bladder of male rats, respectively. Convergent DRG neurons were found in L1-L3 and L6-S2 ganglia with an average distribution of 14% +/- 2%. The resting membrane potential (RMP) of cells isolated from upper lumbar (UL) ganglia was -59.8 +/- 2.7 mV, whereas lumbosacral (LS) neurons were more depolarized (RMP = -49.4 +/- 2.1 mV, P < or = 0.05) under control conditions. Acute trinitrobenzene sulfonic acid (TNBS) colitis (3 days) decreased voltage and current thresholds for action potential firing in LS but not UL convergent capsaicin-sensitive neurons. This effect persisted for 30 days in the absence of overt colonic inflammation. The current threshold for action potential (AP) firing in UL cells was also decreased from 165.0 +/- 24.5 pA (control) to 85.0 +/- 19.1 pA at 30 days (P < or = 0.05), indicating increased excitability. The presence of a subpopulation of colon-bladder convergent DRG neurons and their persistent hyperexcitability after colonic inflammation provides a basis for pelvic organ cross-sensitization.

There is growing appreciation for the importance of gastrointestinal microbiota in many physiological and pathophysiological processes. While morphine and other narcotics are the most widely prescribed therapy for moderate to severe pain clinically, they have been noted to alter microbial composition and promote bacterial translocation to other tissues. Here we examined the pharmacodynamic properties of chronic morphine in mice following bacterial depletion with oral gavage of an antibiotic cocktail (ABX). ABX significantly reduced gut bacteria and prevented chronic morphine induced increases in gut permeability, colonic mucosal destruction, and colonic IL-1β expression. In addition, ABX prevented the development of antinociceptive tolerance to chronic morphine in both the tail-immersion and acetic acid stretch assays. Morphine tolerance was also reduced by oral vancomycin that has 0% bioavailability. These findings were recapitulated in primary afferent neurons isolated from dorsal root ganglia (DRG) innervating the lower gastrointestinal tract, wherein in-vivo administration of ABX prevented tolerance to morphine-induced hypoexcitability. Finally, though ABX repeatedly demonstrated an ability to prevent tolerance, we show that it did not alter susceptibility to precipitation of withdrawal by naloxone. Collectively, these finding indicate that the gastrointestinal microbiome is an important modulator of physiological responses induced by chronic morphine administration.

Chronic opioid use in cirrhosis is associated with increased endotoxemia, dysbiosis and all-cause readmissions.