PKC-mediated inhibitory feedback of the cholecystokinin 1 receptor controls the shape of oscillatory Ca2+signals

Lipids shape brain function through ion channel and receptor modulations: physiological mechanisms and clinical perspectives

Lipids represent the most abundant molecular type in the brain, with a fat content of ∼60% of the dry brain weight in humans. Despite this fact, little attention has been paid to circumscribe the dynamic role of lipids in brain function and disease. Membrane lipids such as cholesterol, phosphoinositide, sphingolipids, arachidonic acid, and endocannabinoids finely regulate both synaptic receptors and ion channels that ensure critical neural functions. After a brief introduction on brain lipids and their respective properties, we review here their role in regulating synaptic function and ion channel activity, action potential propagation, neuronal development, and functional plasticity and their contribution in the development of neurological and neuropsychiatric diseases. We also provide possible directions for future research on lipid function in brain plasticity and diseases.

A Tale of two receptors

Calcium (Ca²⁺) oscillations in hepatocytes have a wide dynamic range. In particular, recent experimental evidence shows that agonist stimulation of the P2Y family of receptors leads to qualitatively diverse Ca²⁺ oscillations. We present a new model of Ca²⁺ oscillations in hepatocytes based on these experiments to investigate the mechanisms controlling P2Y-activated Ca²⁺ oscillations. The model accounts for Ca²⁺ regulation of the IP₃ receptor (IP₃R), the positive feedback from Ca²⁺ on phospholipase C (PLC) and the P2Y receptor phosphorylation by protein kinase C (PKC). Furthermore, PKC is shown to control multiple cellular substrates. Utilising the model, we suggest the activity and intensity of PLC and PKC necessary to explain the qualitatively diverse Ca²⁺ oscillations in response to P2Y receptor activation.

Contributing mechanisms underlying desensitization of cholecystokinin-induced activation of primary nodose ganglia neurons

Cholecystokinin (CCK) is a gut-derived peptide that potently promotes satiety and facilitates gastric function in part by activating G protein-coupled CCK1 receptors on primary vagal afferent neurons. CCK signaling is dynamic and rapidly desensitizes, due to decreases in either receptor function and the resulting signal cascade, ion channel effectors, or both. Here we report a decay-time analytical approach using fluorescent calcium imaging that relates peak and steady-state calcium responses in dissociated vagal afferent neurons, enabling discrimination between receptor and ion channel effector functions. We found desensitization of CCK-induced activation was predictable, consistent across cells, and strongly concentration dependent. The decay-time constant (tau) was inversely proportional to CCK concentration, apparently reflecting the extent of receptor activation. To test this possibility, we directly manipulated the ion channel effector(s) with either decreased bath calcium or the broad-spectrum pore blocker ruthenium red. Conductance inhibition diminished the magnitude of the CCK responses without altering decay kinetics, confirming changes in tau reflect changes in receptor function selectively. Next, we investigated the contributions of the PKC and PKA signaling cascades on the magnitude and decay-time constants of CCK calcium responses. While inhibition of either PKC or PKA increased CCK calcium response magnitude, only general PKC inhibition significantly decreased the decay-time constant. These findings suggest that PKC alters CCK receptor signaling dynamics, while PKA alters the ion channel effector of the CCK response. This analytical approach should prove useful in understanding receptor/effector changes underlying acute desensitization of G-protein coupled signaling and provide insight into CCK receptor dynamics.

Inhibition of Suicidal Erythrocyte Death by Chronic Hypoxia

Background/Aims: High-altitude polycythemia is defined by the increase of hematocrit and hemoglobin at high altitudes caused by production of excessive erythrocytes. Eryptosis is a process by which mature erythrocytes undergo self-destruction sharing several features with apoptosis. However, the eryptosis in high-altitude hypobaric hypoxia is unknown. Thus, the main purpose of this study was to investigate whether chronic hypoxia affected eryptosis and, if so, by what mechanisms. Methods: Biotin labeling technology was utilized to study the survival of red blood cells in chronic hypoxia. Flow cytometry was used to determine the volume of mature erythrocytes from forward scatter, phosphatidylserine scrambling from annexin-V-binding, intracellular Ca²⁺ from Fluo-3-AM, reactive oxygen species (ROS) abundance from ROS-probe, and ceramide and CD47 abundance utilizing specific antibodies. Results: The volume of mature erythrocytes was significantly changed, and the percentage of annexin-V-binding cells was significantly decreased under chronic hypobaric hypoxia. Erythrocyte survival was improved under chronic hypoxia, and chronic hypoxia resulted in a decrease in intracellular Ca²⁺ in vivo and influenced eryptosis which was induced by the Ca²⁺-ionophore ionomycin (1 μM, 60 minutes) in vitro. Chronic hypoxia also resulted in an increase in CD47 and ceramide abundance, but it had no effect on ROS formation. Conclusions: Chronic hypobaric hypoxia can inhibit eryptosis by decreasing intracellular Ca²⁺ and increasing integrin-associated protein CD47.

Tamoxifen: A Protein Kinase C Inhibitor to Treat Mania: A Systematic Review and Meta-Analysis of Randomized, Placebo-Controlled Trials

OBJECTIVE

The aim of this study was to conduct a systematic review of literature to retrieve all randomized controlled trials that evaluated the efficacy of tamoxifen on manic mood episodes and meta-analyze their quantitative results.

METHODS

Four electronic databases were systematically searched from their inception to March 2014: PubMed, Cochrane Library (Cochrane Central Register of Controlled Trials), Scopus, and PsychINFO. Pooled difference in means of changes in mania scores and pooled odds ratio of treatment response (for tamoxifen monotherapy) were calculated as the main effect size. A random effects model was used to pool the data across studies. Quantitative syntheses were expressed by forest plots.

RESULTS

Five randomized controlled trials (3 adjunct trials and 2 monotherapy trials) were included. Regarding adjunct tamoxifen, the standardized difference in mean of mania score changes in tamoxifen arm as compared with control arm was 0.669 (95% confidence interval [CI], 0.15-1.189; P = 0.012). Regarding monotherapy, the pooled difference in means of mania score changes in the tamoxifen arm as compared with the placebo arm was 22.09 (95% CI, 20.98-23.192; P < 0.000000001). Pooled odds ratio of response to treatment was 15.36 (95% CI, 2.99-78.73; P = 0.001) in the tamoxifen group as compared with the placebo group.

CONCLUSIONS

Tamoxifen can be considered an effective treatment for manic bipolar patients. Making a conclusion regarding the efficacy and safety for longer periods warrants further studies with a larger sample size and longer follow-up duration.