RESUMO
Phototransduction, the mechanism underlying the electrical response to light in photoreceptor cells, has been thoroughly investigated in Drosophila melanogaster, an essential model in signal transduction research. These cells present a highly specialized photosensitive membrane consisting of thousands of microvilli forming a prominent structure termed a rhabdomere. These microvilli encompass the phototransduction proteins, most of which are transmembrane and exclusively rhabdomeric. Rhabdomere membrane lipids play a crucial role in the activation of the transient receptor potential ionic channels (TRP and TRPL) responsible for initiating the photoresponse. Despite its importance, rhabdomere lipid composition has not been established. We developed a novel preparation enriched in rhabdomere membranes to perform a thorough characterization of the lipidomics of Drosophila rhabdomeres. Isolated eyes (500) were homogenized and subjected to a differential centrifugation protocol that generates a fraction enriched in rhabdomere membrane. Lipids extracted from this preparation were identified and quantified by gas chromatography coupled to mass spectrometry. We found an abundance of low sterol esters (C16:0, C18:0), highly abundant and diverse triglycerides, free fatty acids, a moderate variety of mono and diacyglycerols (C:16:0, 18:0, C18:1) and abundant phospholipids (principally C18:2). This preparation opens a new avenue for investigating essential aspects of phototransduction.
Assuntos
Animais , Proteínas de Drosophila/química , Drosophila melanogaster/química , Ácidos Graxos/análise , Microvilosidades/química , Células Fotorreceptoras de Invertebrados/química , Canais de Potencial de Receptor Transitório/química , Proteínas de Drosophila/análise , Transdução de Sinal Luminoso/fisiologia , Transporte Proteico/fisiologia , Canais de Potencial de Receptor Transitório/análiseRESUMO
Invertebrate visual transduction involves a second messenger cascade process that leads to an increase in membrane conductance. The identity of the second messenger that gates the light-dependent channels is presently a major focus of attention. Cyclic GMP, inositol trisphosphate and Ca2+ are the most likely candidates for being such a messenger in the species studied so far. Here we review the available evidence for each of these molecules