DUAL ROLE FOR EXTRACELLULAR CALCIUM IN BLOWFLY PHOTOTRANSDUCTION

1. The effect of inhibiting Ca2+-entry during phototransduction in the compound eye of Calliphora vicina has been investigated in a newly developed semi-intact preparation. Simultaneous measurements were made of the receptor potential and the light-induced mitochondrial activation while changing the composition of the extracellular fluid. 2. Lowering the extracellular calcium concentration with EGTA: (i) slows down the kinetics of excitation until the peak of the receptor potential is completely suppressed; and (ii) induces a collapse of the plateau phase after 1 s, although illumination continues. Both effects are reversible. 3. Superfusing the preparation with Ringer solution containing the Ca2+-antagonist Co2+ initially only affects the peak. Prolonged superfusion with Co2+ reduces both the peak and the plateau phase. The latter effect of Co2+ is similar to introduction of Co2+ into the cell via the recording pipette, suggesting that these effects are due to Co2+-entry. These effects of Co2+ are irreversible. 4. The results with EGTA and Co2+ are compared with the reported effect of the Ca2+-antagonist La3+, which induces a collapse of the plateau phase while leaving the peak relatively unaffected. It is suggested that two [Ca2+]e-dependent processes contribute to blowfly phototransduction. Both processes are sensitive to EGTA, whereas Co2+ affects only one and La3+ the other. 5. In the presence of EGTA or Co2+ the light-induced mitochondrial activation was inhibited. This result supports the hypothesis that upon illumination a rise in the intracellular calcium concentration activates mitochondrial respiration

IL-6 induces PI 3-kinase and nitric oxide-dependent protection and preserves mitochondrial function in cardiomyocytes.

OBJECTIVE: Interleukin-6 (IL-6) is a pro-inflammatory cytokine which is a prognostic marker associated with left ventricular contractile dysfunction and heart failure. On the other hand, IL-6 activates signalling pathways which mediate delayed ischemic preconditioning. We have therefore studied the cellular mechanisms of IL-6-induced cardioprotection. METHODS: Inducible nitric oxide synthase (iNOS) expression, cardiomyocyte calcium handling, mitochondrial energetics, and the activation of protective signalling pathways in response to IL-6 were studied in a model of simulated ischemia/reperfusion (sI/R) in isolated neonatal rat ventricular cardiomyocytes. RESULTS: Reperfusion after sI/R induced a rise in cytosolic [Ca2+], a loss of cell morphology and integrity, and a transient increase in mitochondrial potential (Deltapsi m), followed by mitochondrial swelling and collapse of Deltapsi m. Pre-treatment of cardiomyocytes with 10 ng/ml IL-6 for 6 h, 24 h prior to sI/R prevented the secondary rise in cytosolic [Ca2+] and induced expression of iNOS and NO-dependent protection against sI/R injury. The protection against sI/R was concomitant with a NO-dependent reduction in the amplitude of cytosolic Ca2+ transients. IL-6 induced an increase in inner mitochondrial membrane polarisation and increased mitochondrial Ca2+ loading (rhod-2 fluorescence) at baseline, but prevented the reperfusion-induced changes in mitochondrial function. IL-6 pre-treatment also resulted in activation of the phosphatidylinositol (PI) 3-kinase/Akt pathway, and both iNOS induction and IL-6-dependent protection were blocked by the PI 3-kinase inhibitor wortmannin. CONCLUSION: IL-6 induces a PI 3-kinase and NO-dependent protection of cardiomyocytes, which is associated with alterations in mitochondrial Ca2+ handling, inhibition of reperfusion-induced mitochondrial depolarisation, swelling and loss of structural integrity, and suppression of cytosolic Ca2+ transients

Oxygen-sensing pathway for SK channels in the ovine adrenal medulla

The definitive version is available at www.blackwell-synergy.com1. The intracellular pathways that modulate the opening of oxygen-sensitive ion channels during periods of hypoxia are poorly understood. Different tissues appear to use either NADPH oxidase or a rotenone-sensitive mechanism as an oxygen sensor. The aim of the present study was to identify the oxygen-sensing pathway in the oxygen-sensitive sheep adrenal medullary chromaffin cell (AMCC). 2. The whole-cell patch-clamp technique was used to measure K+ currents in dissociated adult ovine chromaffin cells as well as SK channel currents expressed in the H4IIE cell line. 3. Diphenyliodonium, an inhibitor of NADPH oxidase, had no effect on the hypoxia-evoked closure of K+ channels in primary AMCC, whereas the mitochondrial inhibitor rotenone abolished the hypoxia-evoked response. Both these compounds significantly reduced K+ current amplitude under normoxic conditions. 4. One possible mechanism through which the oxygen sensor may modulate K+ channel activity is by altering the redox state of the cell. In sheep AMCC, altering the redox state by the addition of H2O2 to the extracellular solution increased K+ conductance. 5. The oxygen-sensitive K+ (Ko2) channels in sheep chromaffin cells are from the SK family and the whole-cell conductance of cells expressing mouse SK2 or SK3, but not human SK1, was increased by H2O2 and decreased by the reducing agent dithiothreitol. 6. These studies show that, in sheep AMCC, Ko2 channels are modulated via a rotenone-sensitive mechanism and that alteration of the cellular redox state mimics the change produced by alterations in Po2. In a heterologous expression system, SK2 and SK3 channels, the channels that initiate hypoxia-evoked changes in AMCC function, are modulated appropriately by changes in cellular redox state.Damien J Keating, Grigori Y Rychkov, Paul Giacomin and Michael L Robert

Eating in the Elderly

International audienceAlthough having a good diet is recognized to be important for successful aging, malnutrition is one of the highest threats to the health, autonomy, and well-being of older adults. Several medical associations and public policies have proposed dietary guidelines directed at elderly people to ensure a healthy nutritional status and prevent the onset of disease. However, several studies have demonstrated the inadequacy of food intake in the elderly population. A decline in energy and protein intake is frequently observed with aging, in particular for the very old and/or dependent people. The aging process, even when it takes place normally, is associated with several changes likely to have an impact on food intake and the nutritional status of the elderly people such as impairment in appetite regulation, oral health, and chemosensory perception. Beyond these changes, the life of an elderly individual is marked by “breaking points” which may have a social origin (e.g., retirement, widowhood, fall in income) or a medical origin (e.g., onset of a disease, dementia). These breaking points are likely to disrupt their lifestyle habits and in particular their eating habits, leading to new eating habits, which are sometimes inappropriate and at the origin of unbalanced diet. In the context of an aging population, it is therefore crucial to combine meal interventions and food development with nutritional strategies to stimulate appetite and sustain food intake in the older individuals, in order to support active and healthy aging