Thimerosal-induced Ca2+ mobilization in isolated guinea pig cochlear outer hair cells.
Intracellular calcium mobilization of isolated guinea pig cochlear outer hair cells (OHCs) was investigated using thimerosal, a -SH group oxidizing agent, and fura-2 fluorescence ratio imaging microscopy. In the presence of thimerosal, intracellular Ca2+ concentrations ([Ca2+]i) of OHCs were elevated in a dose-dependent manner. Even in Ca(2+)-free medium, Ca2+ response was still induced. The effects of thimerosal on [Ca2+]i were completely blocked and reversed by dithiothreiotol (DTT). Neither 1-100 microM ryanodine nor 5-20 mM caffeine altered the effects of thimerosal. Pretreatment with pertussis toxin (PTX) for 30 min did not affect the thimerosal-induced increase in [Ca2+]i. The increase in [Ca2+]i when Ca2+ was added during thimerosal application in Ca(2+)-free medium was almost completely blocked by 500 microM LaCl3, while nifedipine did not inhibit further increase in [Ca2+]i caused by thimerosal. Thus, oxidation of the -SH group of the OHC membrane can induce a Ca2+ release from intracellular Ca2+ stores, which are ryanodine- and caffeine-insensitive, and Ca2+ influx through non-specific Ca2+ channels, but not the nifedipine-sensitive Ca2+ channels. The possible oxidation of -SH group gated Ca2+ channels in OHCs is worthy of further study.
Chen
L
L
Department of Otolaryngology, Kansai Medical University, Osaka, Japan.
Harada
N
N
Yamashita
T
T
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004229:Dithiothreitol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D018072:Hair Cells, Auditory, Outer / Q000187:drug effects* / Q000378:metabolism; D066298:In Vitro Techniques; D007811:Lanthanum / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology; D013849:Thimerosal / Q000008:administration & dosage / Q000494:pharmacology*
D012433:Ryanodine; D013849:Thimerosal; D002110:Caffeine; D007811:Lanthanum; D002118:Calcium; D004229:Dithiothreitol