Efferent neurotransmitters and intracellular Ca2+ concentrations in inner hair cells of guinea pig.
To elucidate efferent inhibitory mechanisms of the cochlear inner hair cells (IHCs), the effects of candidate efferent neurotransmitters on intracellular Ca2+ concentrations ([Ca2+]i) in the isolated IHCs of 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 and reversible increase in [Ca2+]i. In the presence of 10 microM ATP, there was a rapid and marked rise in [Ca2+]i. Thus, both ACh and ATP seem to be efferent neurotransmitters in IHCs of guinea pig. The ATP-induced elevation of [Ca2+]i in IHCs was suppressed when ACh was concomitantly applied; therefore, ACh may act as an antagonist of ATP-induced Ca2+ entry. With the independent addition of 10 microM calcitonin gene-related peptide and 10 microM enkephalin, there were no significant increases in [Ca2+]i. These neuropeptides are putative candidates for the efferent neuromodulators in IHCs of the guinea pig.
Yamashita
T
T
Department of Otolaryngology, Kansai Medical University, Osaka, Japan.
Amano
H
H
Kumazawa
T
T
D000109:Acetylcholine / Q000502:physiology; D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000502:physiology; D002118:Calcium / Q000502:physiology*; D004745:Enkephalins / Q000502:physiology; D016257:Fura-2 / Q000494:pharmacology; D006168:Guinea Pigs; D006199:Hair Cells, Auditory, Inner / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D009476:Neurons, Efferent / Q000502:physiology; D018377:Neurotransmitter Agents / Q000502:physiology*; D013569:Synapses / Q000502:physiology
D004745:Enkephalins; D018377:Neurotransmitter Agents; D000255:Adenosine Triphosphate; D015740:Calcitonin Gene-Related Peptide; D000109:Acetylcholine; D002118:Calcium; D016257:Fura-2