Taste Modulators are Tools to Gain a Better Insight into Specific Sensitivity of Chemoreceptors in Blowflies

Abstract

One of the questions arising in studying taste transduction is whether natural sweets are distinguished from sweeteners as the former are the major source of metabolic energy. Blowflies are a convenient preparation to study chemoreception, given their relatively simplicity, availability and the vast body of related work published. The labellar chemosensory system of blowflies consists of sensilla housing four chemoreceptive neurons, named ‘salt’, ‘sugar’, ‘water’ and ‘deterrent’ cells after their best recognized stimuli. While spike activity from these sensory neurons is readily recordable, dendrite membranes remain difficult to access (Murakami and Kijima, 2000), making the mechanism(s) of transduction little understood at the membrane level. However, information can be obtained by studying the effects on the spike activity of specific pharmacological modulators used in association with chemical stimuli. The sugar receptor cell is capable of detecting a broad variety of substances, such as pyranose or furanose sugars, as well as amino acids and proteins. On the other hand, Ahamed et al. (2001) found that the sweetener glycyrrhizin activates the ‘pyranose site’ of the ‘sugar’ cell membrane in Phormia regina, while Na-saccharine stimulates the ‘deterrent cell’ in Protophormia terraenovae (Liscia et al., 2004). Calcium ions appear to be in many ways involved in the transduction mechanisms of various tastants. We therefore decided to investigate the role of calcium in the chemoreception mechanism(s) of sugars and sweeteners. In the present study we have specifically investigated the reception mechanism of a natural pyranose sugar (sucrose) and a commonly used sweetener for humans (Na-cyclamate) by addressing such issues as the involvement of Ca2+ cascade and/or of Ca2+ channels in the sugar transduction mechanism.