Inhibition of Ion Channels and Heart Beat in Drosophila by Selective COX-2 Inhibitor SC-791

Recent findings suggest that modulation of ion channels might be implicated in some of the clinical effects of coxibs, selective inhibitors of cyclooxygenase-2 (COX-2). Celecoxib and its inactive analog 2,5-dimethyl-celecoxib, but not rofecoxib, can suppress or augment ionic currents and alter functioning of neurons and myocytes. To better understand these unexpected effects, we have recently investigated the mechanism of inhibition of human Kv2.1 channels by a highly selective COX-2 inhibitor SC-791. In this study we have further explored the SC-791 action on ion channels and heartbeat in Drosophila, which lacks cyclooxygenases and thus can serve as a convenient model to study COX-2-independent mechanisms of coxibs. Using intracellular recordings in combination with a pharmacological approach and utilizing available Drosophila mutants, we found that SC-791 inhibited voltage-activated K+ and L-type Ca2+ channels in larval body-wall muscles and reduced heart rate in a concentration-dependent manner. Unlike celecoxib and several other K+ channel blockers, SC-791 did not induce arrhythmia. Instead, application of SC-791 resulted in a dramatic slowing of contractions and, at higher concentrations, in progressively weaker contractions with gradual cessation of heartbeat. Isradipine, a selective blocker of L-type Ca2+ channels, showed a similar pattern of heart arrest, though no prolongation of contractions was observed. Ryanodine was the only channel modulating compound of those tested additionally that was capable of slowing contractions. Like SC-791, ryanodine reduced heart rate without arrhythmia. However, it could not stop heartbeat completely even at 500 µM, the highest concentration used. The magnitude of heart rate reduction, when SC-791 and ryanodine were applied together, was smaller than expected for independent mechanisms, raising the possibility that SC-791 might be interfering with excitation-contraction coupling in Drosophila heart

Response to Mechanical Stress Is Mediated by the TRPA Channel Painless in the Drosophila Heart

Mechanotransduction modulates cellular functions as diverse as migration, proliferation, differentiation, and apoptosis. It is crucial for organ development and homeostasis and leads to pathologies when defective. However, despite considerable efforts made in the past, the molecular basis of mechanotransduction remains poorly understood. Here, we have investigated the genetic basis of mechanotransduction in Drosophila. We show that the fly heart senses and responds to mechanical forces by regulating cardiac activity. In particular, pauses in heart activity are observed under acute mechanical constraints in vivo. We further confirm by a variety of in situ tests that these cardiac arrests constitute the biological force-induced response. In order to identify molecular components of the mechanotransduction pathway, we carried out a genetic screen based on the dependence of cardiac activity upon mechanical constraints and identified Painless, a TRPA channel. We observe a clear absence of in vivo cardiac arrest following inactivation of painless and further demonstrate that painless is autonomously required in the heart to mediate the response to mechanical stress. Furthermore, direct activation of Painless is sufficient to produce pauses in heartbeat, mimicking the pressure-induced response. Painless thus constitutes part of a mechanosensitive pathway that adjusts cardiac muscle activity to mechanical constraints. This constitutes the first in vivo demonstration that a TRPA channel can mediate cardiac mechanotransduction. Furthermore, by establishing a high-throughput system to identify the molecular players involved in mechanotransduction in the cardiovascular system, our study paves the way for understanding the mechanisms underlying a mechanotransduction pathway

Resolution and pharmacological analysis of the voltage-dependent calcium channels of Drosophila larval muscles

Voltage-dependent calcium channels play a role in many cellular phenomena. Very little is known about Ca2+ channels in Drosophila, especially those in muscles. Existing literature on neuronal Ca2+ channels of Drosophila suggests that their pharmacology may be distinct from that of vertebrate Ca2+ channels. This raises questions on the pharmacology and diversity of Ca2+ channels in Drosophila muscles. Here we show that the Ca2+ channel current in the body-wall muscles of Drosophila larvae consists of two main components. One component is sensitive to 1,4-dihydropyridines and diltiazem, which block vertebrate L-type Ca2+ channels. The second component is sensitive to amiloride, which blocks vertebrate T-type Ca2+ channels. In contrast to Drosophila brain membrane preparations in which a majority of the Ca2+ channels are phenylalkylamine-sensitive but dihydropyridine-insensitive, the major current in the muscles was dihydropyridine-sensitive but relatively less sensitive to verapamil. This might indicate an underlying tissue specific distribution of distinct subtypes of dihydropyridine/phenylalkylamine-sensitive Ca2+ channels in Drosophila. Low verapamil sensitivity of the dihydropyridine-sensitive current of Drosophila muscles also set it apart from the vertebrate L-type channels which are sensitive to 1,4-dihydropyridines, benzothiazepines as well as phenylalkylamines. The dihydropyridine-sensitive current in Drosophila muscles activated in a similar voltage range as the vertebrate L-type current. As with the vertebrate current, blockade by dihydropyridines was voltage dependent.</jats:p

Honeybee locomotion is impaired by Am-CaV3 low voltage-activated Ca(2+) channel antagonist.

Voltage-gated Ca(2+) channels are key transducers of cellular excitability and participate in several crucial physiological responses. In vertebrates, 10 Ca(2+) channel genes, grouped in 3 families (CaV1, CaV2 and CaV3), have been described and characterized. Insects possess only one member of each family. These genes have been isolated in a limited number of species and very few have been characterized although, in addition to their crucial role, they may represent a collateral target for neurotoxic insecticides. We have isolated the 3 genes coding for the 3 Ca(2+) channels expressed in Apis mellifera. This work provides the first detailed characterization of the honeybee T-type CaV3 Ca(2+) channel and demonstrates the low toxicity of inhibiting this channel. Comparing Ca(2+) currents recorded in bee neurons and myocytes with Ca(2+) currents recorded in Xenopus oocytes expressing the honeybee CaV3 gene suggests native expression in bee muscle cells only. High-voltage activated Ca(2+) channels could be recorded in the somata of different cultured bee neurons. These functional data were confirmed by in situ hybridization, immunolocalization and in vivo analysis of the effects of a CaV3 inhibitor. The biophysical and pharmacological characterization and the tissue distribution of CaV3 suggest a role in honeybee muscle function

"King archie, who was quite grouchy" - a vocal dysphonia health education project O rei Sebastião que era muito resmungão

PURPOSE: one major cause of dysphonia can be linked to the presence of vocal folds nodules - a condition commonly seen in children due to vocal misuse and/or vocal abuse. The present health education project, also directed to parents and educators, aims at making children (the project's chief target-population) aware of how to make a correct use of their voice. METHOD: the target population includes parents, educators and children from both sexes and aged between five and eight years old. RESULT: a health education initiative was developed, which main instrument consists in a children's literature book, supplemented by an interactive CD. The instrument relies on a simple and easy-to-follow story where the issue of child dysphonia is addressed. CONCLUSIONS: the developed health education instrument is substantial for its chief target-population; it works as a suitable vehicle for promoting, in children, access, sensibility and awareness regarding aspects of one's voice one should be attentive to

Characterization of the first honeybee Ca2+ channel subunit reveals two novel species- and splicing-specific modes of regulation of channel inactivation

International audienceThe honeybee is a model system to study learning and memory, and Ca2+ signals play a key role in these processes. We have cloned, expressed, and characterized the first honeybee Ca2+ channel subunit. We identified two splice variants of the Apis CaVβ Ca2+ channel subunit (Am-CaVβ) and demonstrated expression in muscle and neurons. Although AmCaVβ shares with vertebrate CaVβ subunits the SH3 and GK domains, it beholds a unique N terminus that is alternatively spliced in the first exon to produce a long (a) and short (b) variant. When expressed with the CaV2 channels both, AmCaVβa and AmCaVβb, increase current amplitude, shift the voltage-sensitivity of the channel, and slow channel inactivation as the vertebrate CaVβ2a subunit does. However, as opposed to CaVβ2a, slow inactivation induced by Am-CaVβa was insensitive to palmitoylation but displayed a unique PI3K sensitivity. Inactivation produced by the b variant was PI3K-insensitive but staurosporine/H89-sensitive. Deletion of the first exon suppressed the sensitivity to PI3K inhibitors, staurosporine, or H89. Recording of Ba2+ currents in Apis neurons or muscle cells evidenced a sensitivity to PI3K inhibitors and H89, suggesting that both AmCaVβ variants may be important to couple cell signaling to Ca2+ entry in vivo. Functional interactions with phospho-inositide and identification of phosphorylation sites in AmCaVβa and AmCaVβb N termini,respectively, suggest that AmCaVβ splicing promoted two novel and alternative modes of regulation of channel activity with specific signaling pathways. This is the first description of a splicing-dependent kinase switch in the regulation of Ca2+ channel activity by CaVβ subunit