American journal of physiology. Cell physiology
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Am. J. Physiol., Cell Physiol. · Jun 2010
Dynamic changes in the TRPA1 selectivity filter lead to progressive but reversible pore dilation.
TRPA1 is a nonselective cation channel belonging to the transient receptor potential (TRP) family that is expressed in peripheral sensory neurons and may play important roles in pain perception and inflammation. We found that agonist stimulation of TRPA1, along with other members of the TRP family (TRPV1-4 and TRPM8), can induce the appearance of a large pore permeable to large organic cations such as Yo-Pro (YP) and N-methyl-d-glucamine, in an agonist and divalent cation-dependent manner. ⋯ Our data suggest that changes in the TRP channel selectivity filter itself result in a progressive but reversible pore dilation process, a process that is under strong regulation by external calcium ions. Our data suggest that calcium plays a novel role in setting the amount of time TRPA1 channels spend in a dilated state providing a mechanism that may limit sensory neuron activation by painful or irritating substances.
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Am. J. Physiol., Cell Physiol. · Apr 2010
Dysregulation of lipolysis and lipid metabolism in visceral and subcutaneous adipocytes by high-fat diet: role of ATGL, HSL, and AMPK.
This study investigated the molecular mechanisms by which a high-fat diet (HFD) dysregulates lipolysis and lipid metabolism in mouse epididymal (visceral, VC) and inguinal (subcutaneous, SC) adipocytes. Eight-weeks of HFD feeding increased adipose triglyceride lipase (ATGL) content and comparative gene identification-58 (CGI-58) expression, whereas hormone-sensitive lipase (HSL) phosphorylation and perilipin content were severely reduced. Adipocytes from HFD mice elicited increased basal but blunted epinephrine-stimulated lipolysis and increased diacylglycerol content in both fat depots. ⋯ However, in HFD subcutaneous adipocytes, forskolin induced lipolysis without detectable HSL phosphorylation, suggesting activation of an alternative lipase in response to HFD-induced suppression of HSL in VC and SC adipocytes. HFD also powerfully inhibited basal, epinephrine-, and forskolin-induced AMP kinase (AMPK) activation as well peroxisome proliferator-activated receptor gamma coactivator-1alpha expression, citrate synthase activity, and palmitate oxidation in both fat depots. In summary, novel evidence is provided that defective adrenergic receptor signaling combined with upregulation of ATGL and suppression of HSL and AMPK signaling mediate HFD-induced alterations in lipolysis and lipid utilization in VC and SC adipocytes, which may play an important role in defective lipid mobilization and metabolism seen in diet-induced obesity.
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Am. J. Physiol., Cell Physiol. · Mar 2010
CCK activates RhoA and Rac1 differentially through Galpha13 and Galphaq in mouse pancreatic acini.
Cholecystokinin (CCK) has been shown to activate RhoA and Rac1, as well as reorganize the actin cytoskeleton and, thereby, modify acinar morphology and amylase secretion in mouse pancreatic acini. The aim of the present study was to determine which heterotrimeric G proteins activate RhoA and Rac1 upon CCK stimulation. Galpha(13), but not Galpha(12), was identified in mouse pancreatic acini by RT-PCR and Western blotting. ⋯ Together, these findings indicate that, in mouse pancreatic acini, Galpha(13) links CCK stimulation to the activation of RhoA, whereas both Galpha(13) and Galpha(q) link CCK stimulation to the activation of Rac1. CCK-induced actin cytoskeletal reorganization is mainly mediated by Galpha(q). By contrast, Galpha(13) and Galpha(q) signaling are required for CCK-induced amylase secretion.