EFFECTS OF EFFERENT NEUROTRANSMITTERS ON INTRACELLULAR CA-2+ CONCENTRATION IN VESTIBULAR HAIR-CELLS OF THE GUINEA-PIG

The effects of putative efferent neurotransmitters on intracellular Ca2+ concentration ([Ca2+]i) in isolated vestibular hair cells (VHCs) of the guinea pig were determined using the Ca2+ sensitive dye Fura-2 and digital imaging microscopy. In the presence of 1 mM acetylcholine (ACh) there was a gradual increase in [Ca2+]i. In the presence of 10 muM ATP there was a rapid rise in [Ca2+]i. Thus, both ACh and ATP seem to be efferent neurotransmitters in VHCs of the guinea pig. When 100 muM Gamma-aminobutyric acid (GABA) was added them was a rapid increase in [Ca2+]i; thus GABA also seems to be an efferent neurotmnsmitter in VHCs. With the independent addition of 10 muM calcitonin gene-related peptide and 10 muM M- and L-enkephalin there were no significant increase in [Ca2+]i. We presume that these neuropeptides were functioning as efferent neuromodulators rather than as neurotransmitters.