ABSTRACT
1. Typical adenylate cyclase (AC) responses to guanine nucleotides were found in membranes of pig circumvallate (CV) taste papillae. 2. Sucrose stimulated AC activity in the CV membranes and this stimulation was GTP dependent and tissue specific. 3. The stimulatory effect of sucrose in the CV membranes was dependent on the concentration of membranes used in the AC assay. 4. This study provides the first biochemical data on cellular transduction of taste in the pig, compares positively to preliminary results in cattle and supports recent suggestions for a role of cAMP in sweet taste transduction.
Subject(s)
Adenylyl Cyclases/metabolism , Sucrose/physiology , Taste Buds/enzymology , Animals , Cattle , Cell Membrane/enzymology , Enzyme Activation , Female , Male , Swine , Taste Buds/ultrastructureABSTRACT
The non-nutritive sweetener, saccharin, was found to stimulate significantly the activity of adenylate cyclase in membranes derived from skeletal muscle of rat. Sodium saccharin enhanced adenylate cyclase activity in a dose-related manner, and this activation appeared to be dependent on the presence of guanine nucleotides, suggesting the involvement of GTP-binding proteins. In membranes derived from the liver, however, sodium saccharin had an effect which was dependent on the concentration of membranes used in the adenylate cyclase assay. In high concentrations of membranes, sodium saccharin had a stimulatory effect, while in low concentration an inhibition was observed.
Subject(s)
Adenylyl Cyclases/metabolism , Liver/drug effects , Muscles/drug effects , Saccharin/pharmacology , Animals , Cell Membrane/drug effects , Cell Membrane/enzymology , Guanosine Triphosphate/pharmacology , In Vitro Techniques , Liver/cytology , Liver/enzymology , Muscles/cytology , Muscles/enzymology , RatsABSTRACT
Sucrose and other saccharides, which produce an appealing taste in rats, were found to significantly stimulate the activity of adenylate cyclase in membranes derived from the anterior-dorsal region of rat tongue. In control membranes derived from either tongue muscle or tongue non-sensory epithelium, the effect of sugars on adenylate cyclase activity was either much smaller or absent. Sucrose enhanced adenylate cyclase activity in a dose-related manner, and this activation was dependent on the presence of guanine nucleotides, suggesting the involvement of a GTP-binding protein ('G-protein'). The activation of adenylate cyclase by various mono- and di-saccharides correlated with their electrophysiological potency. Among non-sugar sweeteners, sodium saccharin activated the enzyme, whereas aspartame and neohesperidin dihydrochalcone did not, in correlation with their sweet-taste effectiveness in the rat. Sucrose activation of the enzyme was partly inhibited by Cu2+ and Zn2+, in agreement with their effect on electrophysiological sweet-taste responses. Our results are consistent with a sweet-taste transduction mechanism involving specific receptors, a guanine-nucleotide-binding protein and the cyclic AMP-generating enzyme adenylate cyclase.
