Biological characteristics of the globular substance in the otoconial membrane of the guinea pig

Abstract

Biological characteristics of the globular substance, which is considered to be a precursor of otoconia, were investigated by means of confocal laser scanning microscopy. The shape of the globular substance was a complete sphere, 3–10 μm in diameter. Its surface stained positively with both rhodamine 123 and DiOC 6(3), implying similarity to intracellular organelles, whereas no fluorescence was seen when stained with chlortetracycline, a membrane-associated Ca 2+ dye. Meanwhile, this substance showed very little affinity for six kinds of lectins, indicating the lack of a surface structure of carbohydrates. The fluorescence of fluo-3 in the globular substance increased markedly after the application of ionomycin. But this was completely inhibited by the depletion of external Ca 2+. This reaction suggests that the surface of the globular substance exhibits characteristics of a biological membrane and that the influx of external Ca 2+ occurs through membrane-combined ionomycin. Internal free Ca 2+ concentration varied from 1.1×10 −9 to 1.6×10 t-4M, the geometric mean being 3.3×10 −7 M, which is higher than normal resting level of intracellular Ca 2+ concentration but lower than the calcium content of the globular substance estimated by X-ray microanalysis in previous studies.