Taicatoxin inhibits the calcium-dependent slow motility of mammalian outer hair cells

The effects of taicatoxin on the slow motility of isolated outer hair cells of guinea pig were studied in the experiments. Pretreatment with taicatoxin (0.19 μM) was able to prevent both the cell shortening induced by high K+ (50 mM), and the cell elongation induced by ionomycin (10 μM). These effects of taicatoxin can be mimicked by pretreatment of cells with Ca2+-free medium on the slow motility in response to ionomycin or high K+. Pretreatment with neither calcium channel blockers such as nifedipine (L-type blocker), ω-conotoxin GVIA (N-type blocker), and ω-agatoxin IVA (P-type blocker); nor potassium channel blockers, such as tetraethylammonium chloride (TEA) and 3,4-diaminopyridine (3,4-DAP) can antagonize the cell shortening effect induced by high K+ and cell elongation induced by ionomycin. The calcium-imaging experiment indicated that taicatoxin, but not nifedipine, did prevent an increase of intracellular Ca2+ level significantly induced by high K+. These results demonstrate that the effect of taicatoxin was to block the calcium entry through calcium channels of cell membrane, without relative to its properties of potassium channel blockers. We conclude that taicatoxin-sensitive-calcium channels at least impart, play a significant role in the slow motility of outer hair cell.