title: Effects of protein kinase and phosphatase inhibitors on slow shortening of guinea pig cochlear outer hair cells.
abstract: The intracellular mechanisms of slow shortening in isolated guinea pig cochlear outer hair cells were investigated using inhibitors and/or an activator of protein kinases and protein phosphatases. The slow shortening was induced by tetanic electrical field stimulation, and changes in the cell length, volume and intracellular Cl- concentration were microscopically monitored using a chloride-sensitive fluorescent dye. The slow shortening was inhibited by a calmodulin inhibitor, W-7, and a calcium calmodulin-dependent protein kinase II (CaMKII) inhibitor, KN-62. The inhibition by W-7 or KN-62, was abolished by the supplemented conductance of K+ with valinomycin. Among the protein phosphatase inhibitors tested, a type 1 and 2A protein phosphatase inhibitor, calyculin A, inhibited the slow shortening. The inhibition by calyculin A was abolished by the increased Cl- permeability, but neither by the increased K+ conductance with valinomycin nor by the increased Ca2+ conductance with A23187. A protein serine/threonine phosphatase activator, N-acetylsphingosine, inhibited the shortening, which was abolished by either valinomycin or a type 2A protein phosphatase inhibitor, okadaic acid, but not by calyculin A. These findings suggest the following signaling mechanisms in the slow shortening of outer hair cells; the K+ channel opening is facilitated through protein phosphorylation by CaMKII and suppressed via okadaic acid-sensitive dephosphorylation, and the Cl- channel opening depends on calyculin A-sensitive protein phosphatase activity.
authors.affiliation: Department of Pharmacology, Kansai Medical University, Moriguchi, Osaka 570, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Minamino
authors.forename: M
authors.initials: M
authors.lastname: Hara
authors.forename: S
authors.initials: S
authors.lastname: Ohnishi
authors.forename: T
authors.initials: T
authors.lastname: Irie
authors.forename: T
authors.initials: T
authors.lastname: Yamashita
authors.forename: A
authors.initials: A
authors.lastname: Minato
authors.forename: C
authors.initials: C
authors.lastname: Inagaki
mesh_terms: D000818:Animals; D048429:Cell Size / Q000187:drug effects; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006168:Guinea Pigs; D018072:Hair Cells, Auditory, Outer / Q000166:cytology / Q000187:drug effects*; D066298:In Vitro Techniques; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors; D013997:Time Factors
chemical_list: D004791:Enzyme Inhibitors; D047428:Protein Kinase Inhibitors; D010749:Phosphoprotein Phosphatases