Possible Mediation of G-Proteins in Cold-Sensory Transduction in Paramecium Multimicronucleatum

The possible involvement of G-proteins in cold-sensory transduction was examined using voltage-clamped Paramecium multimicronucleatum into which non-hydrolyzable guanosine nucleotide analogues had been applied intracellularly. Guanosine-5'-O-3-thiotriphosphate, guanosine-5'-O-2-thiodiphosphate and aluminium fluoride all reduced the transient inward current in response to cooling, suggesting the possibility that G-proteins mediate cold-sensory transduction. Internal application of a Ca2+ chelator, EGTA, also reduced the current response. In addition to their effect on reducing the cold-sensory response, application of these chemicals modulated both the resting potential and the membrane conductance. Possible correlations between G-protein activity and the regulation of intracellular Ca2+ levels are discussed.