Effects of efferent neurotransmitters on intracellular Ca2+ 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 microM 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 microM Gamma-aminobutyric acid (GABA) was added there was a rapid increase in [Ca2+]i; thus GABA also seems to be an efferent neurotransmitter in VHCs. With the independent addition of 10 microM calcitonin gene-related peptide and 10 microM 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.
Yamashita
T
T
Department of Otolaryngology, Kansai Medical University, Osaka, Japan.
Ohnishi
S
S
Ohtani
M
M
Kumazawa
T
T
D000109:Acetylcholine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001369:Axons / Q000187:drug effects; D015740:Calcitonin Gene-Related Peptide / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D003712:Dendrites / Q000187:drug effects; D004525:Efferent Pathways / Q000187:drug effects; D004743:Enkephalin, Leucine / Q000494:pharmacology; D004744:Enkephalin, Methionine / Q000494:pharmacology; D006168:Guinea Pigs; D006198:Hair Cells, Auditory / Q000187:drug effects*; D008856:Microscopy, Fluorescence; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D013569:Synapses / Q000187:drug effects; D009435:Synaptic Transmission / Q000187:drug effects*; D014725:Vestibular Nerve / Q000187:drug effects*; D014722:Vestibule, Labyrinth / Q000294:innervation*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D018377:Neurotransmitter Agents; D005680:gamma-Aminobutyric Acid; D004744:Enkephalin, Methionine; D004743:Enkephalin, Leucine; D000255:Adenosine Triphosphate; D015740:Calcitonin Gene-Related Peptide; D000109:Acetylcholine; D002118:Calcium