A naturally occurring membrane-anchored Gαs variant, XLαs, activates phospholipase Cß4.

Extra-large stimulatory Gα (XLαs) is a large variant of G protein αs subunit (Gαs) that uses an alternative promoter and thus differs from Gαs at the first exon. XLαs activation by G protein-coupled receptors mediates cAMP generation, similarly to Gαs; however, Gαs and XLαs have been shown to have distinct cellular and physiological functions. For example, previous work suggests that XLαs can stimulate inositol phosphate production in renal proximal tubules and thereby regulate serum phosphate levels. In this study, we show that XLαs directly and specifically stimulates a specific isoform of phospholipase Cß (PLCß), PLCß4, both in transfected cells and with purified protein components. We demonstrate that neither the ability of XLαs to activate cAMP generation nor the canonical G protein switch II regions are required for PLCß stimulation. Furthermore, this activation is nucleotide independent but is inhibited by Gßγ, suggesting a mechanism of activation that relies on Gßγ subunit dissociation. Surprisingly, our results indicate that enhanced membrane targeting of XLαs relative to Gαs confers the ability to activate PLCß4. We also show that PLCß4 is required for isoproterenol-induced inositol phosphate accumulation in osteocyte-like Ocy454 cells. Taken together, we demonstrate a novel mechanism for activation of phosphoinositide turnover downstream of Gs-coupled receptors that may have a critical role in endocrine physiology.

Electrochemical Measurement of Dopamine Release and Uptake in Zebrafish Following Treatment with Carboplatin.

Post-chemotherapy cognitive impairment, also known as 'chemobrain,' is a neurological condition in which cognitive function is impaired as a result of cancer chemotherapy treatment. In this work, we used fast-scan cyclic voltammetry (FSCV) to measure electrically evoked dopamine release and uptake in whole brain preparations from zebrafish that have been treated with carboplatin, an agent associated with chemobrain. We administered carboplatin by addition to the fish's tank water or their food. One week of treatment with 100 µM carboplatin in the water was needed to significantly impair dopamine release (∼40 % of control); however, only one day of treatment through the zebrafish's food was needed to cause a similar impairment. Atomic absorption spectroscopy measurements suggested that administration through food resulted in higher initial levels of carboplatin compared to water administration, but water administration resulted in an increase over time. Uptake, determined by modeling stimulated release plots, was unaffected. These results are consistent with our previous findings of diminished neurotransmitter release in rats and support a role for zebrafish in chemobrain-related studies.

Acute altitude-induced hypoxia suppresses plasma glucose and leptin in healthy humans.

To examine the effects of acute altitude-induced hypoxia on the hormonal and metabolic response to ingested glucose, 8 young, healthy subjects (5 men and 3 women; age, 26 +/- 2 years; body mass index, 23.1 +/- 1.0 kg/m(2)) performed 2 randomized trials in a hypobaric chamber where a 75-g glucose solution was ingested under simulated altitude (ALT, 4300 m) or ambient (AMB, 362 m) conditions. Plasma glucose, insulin, C-peptide, epinephrine, leptin, and lactate concentrations were measured at baseline and 30, 60, 90, and 120 minutes after glucose ingestion during both trials. Compared with AMB, the plasma glucose response to glucose ingestion was reduced during the ALT trial (P = .04). There were no differences in the insulin and C-peptide responses between trials or in insulin sensitivity based on the homeostasis model assessment of insulin resistance. Epinephrine and lactate were both elevated during the ALT trial (P < .05), whereas the plasma leptin response was reduced compared with AMB (P < .05). The data suggest that the plasma glucose response is suppressed at ALT, but this is not due to insulin per se because insulin and C-peptide levels were similar for both trials. Elevated plasma epinephrine and lactate during ALT are indicative of increased glycogenolysis, which may have masked the magnitude of the reduced glucose response. We conclude that, during acute altitude exposure, there is a rapid metabolic response that is accompanied by a shift in the hormonal milieu that appears to favor increased glucose utilization.

Venous but not skeletal muscle interstitial nitric oxide is increased during hypobaric hypoxia.

Systemic hypoxia leads to peripheral vasodilation that serves to counteract the decrease in peripheral oxygen (O(2)) delivery. Skeletal muscle vasodilation associated with hypoxia is due to release of vasodilator substances such as adenosine and/or nitric oxide (NO). We hypothesized that skeletal muscle may act as a source of NO during exposure to hypoxia. Therefore, we measured NO in forearm venous plasma and in skeletal muscle interstitial dialysate in seven healthy young men during exposure to simulated altitude of 2,438 and 4,877 m (20 min at each level) in a hypobaric chamber. O(2) saturation (mean +/- SEM) fell from 98.0 +/- 0.2% at ambient conditions to 91.0 +/- 0.4% at 2,438 m and to 73.2 +/- 4.4% at 4,877 m (P < 0.05). While blood pressure remained unchanged, heart rate increased in a graded fashion (P < 0.05). Plasma NO (chemiluminescence method) rose from 11.6 +/- 1.3 to 16.9 +/- 2.9 microM at 2,438 m (P < 0.05) but remained similar at 16.4 +/- 2.3 microM at 4,877 m (NS). In contrast, skeletal muscle microdialysate NO levels were lower than plasma NO (P < 0.01) and did not change during simulated altitude. Thus, hypoxia produced by simulated high altitude exposure leads to an increase in plasma but not skeletal muscle interstitial NO. These data support an important role of NO in the peripheral vascular responses to hypoxia. The differential responses of plasma vs. interstitial NO during hypoxia suggest an endothelial or intravascular source of NO.