Changes of intra-mitochondrial Ca2+ in adult ventricular cardiomyocytes examined using a novel fluorescent Ca2+ indicator targeted to mitochondria.

In this study a Ca(2+) sensitive protein was targeted to the mitochondria of adult rabbit ventricular cardiomyocytes using an adenovirus transfection technique. The probe (Mitycam) was a Ca(2+)-sensitive inverse pericam fused to subunit VIII of human cytochrome c oxidase. Mitycam expression pattern and Ca(2+) sensitivity was characterized in HeLa cells and isolated adult rabbit cardiomyocytes. Cardiomyocytes expressing Mitycam were voltage-clamped and depolarized at regular intervals to elicit a Ca(2+) transient. Cytoplasmic (Fura-2) and mitochondrial Ca(2+) (Mitycam) fluorescence were measured simultaneously under a range of cellular Ca(2+) loads. After 48 h post-adenoviral transfection, Mitycam expression showed a characteristic localization pattern in HeLa cells and cardiomyocytes. The Ca(2+) sensitive component of Mitycam fluorescence was 12% of total fluorescence in HeLa cells with a K(d) of approximately 220 nM. In cardiomyocytes, basal and beat-to-beat changes in Mitycam fluorescence were detected on initiation of a train of depolarizations. Time to peak of the mitochondrial Ca(2+) transient was slower, but the rate of decay was faster than the cytoplasmic signal. During spontaneous Ca(2+) release the relative amplitude and the time course of the mitochondrial and cytoplasmic signals were comparable. Inhibition of mitochondrial respiration decreased the mitochondrial transient amplitude by approximately 65% and increased the time to 50% decay, whilst cytosolic Ca(2+) transients were unchanged. The mitochondrial Ca(2+) uniporter (mCU) inhibitor Ru360 prevented both the basal and transient components of the rise in mitochondrial Ca(2+). The mitochondrial-targeted Ca(2+) probe indicates sustained and transient phases of mitochondrial Ca(2+) signal, which are dependent on cytoplasmic Ca(2+) levels and require a functional mCU.

Metabolomic profiling of Drosophila using liquid chromatography Fourier transform mass spectrometry.

Hydrophilic interaction chromatography (HILIC) interfaced with an Orbitrap Fourier transform mass spectrometer (FT-MS) was used to carry out metabolomic profiling of the classical Drosophila mutation, rosy (ry). This gene encodes a xanthine oxidase/dehydrogenase. In addition to validating the technology by detecting the same changes in xanthine, hypoxanthine, urate and allantoin that have been reported classically, completely unsuspected changes were detected in each of the tryptophan, arginine, pyrimidine and glycerophospholipid metabolism pathways. The rosy mutation thus ramifies far more widely than previously detected.

Insect renal tubules constitute a cell-autonomous immune system that protects the organism against bacterial infection.

Innate immunity is a widespread and important defence against microbial attack, which in insects is thought to originate mainly in the fat body. Here we demonstrate that the fluid-transporting Malpighian (renal) tubule of Drosophila melanogaster constitutes an autonomous immune-sensing tissue utilising the nitric oxide (NO) signalling pathway. Reverse transcriptase PCR (RT-PCR) shows that tubules express those genes encoding components of the Imd pathway. Furthermore, isolated tubules bind and respond to lipopolysaccharide (LPS), by upregulating anti-microbial peptide (diptericin) gene expression and increased bacterial killing. Excised, LPS-challenged tubules, as well as tubules from LPS-infected flies, display increased NO synthase (NOS) activity upon immune challenge. Targetted expression of a Drosophila NOS (dNOS) transgene to only principal cells of the tubule main segment using the GAL4/UAS system increases diptericin expression. In live flies, such targetted over-expression of dNOS to tubule principal cells confers increased survival of the whole animal upon E. coli challenge. Thus, we describe a novel role of Malpighian tubules in immune sensing and insect survival.