The distribution of the calcium buffer calbindin in the cochlea of the guinea-pig

INTRODUCTION: Ca2+ is involved in many important functions in the inner ear and its intracellular levels are controlled by extrusion mechanisms and stores, and also by buffers such as calbindin. The latter has been demonstrated previously in hair cells of the organ of Corti using immunofluorescence at the light microscopic level, although its precise intracellular distribution has yet to be determined. One postulated role for calbindin in the brain is protection against hypoxic cell injury and degeneration, in which Ca2+ overload has been implicated. METHODS: We have therefore performed postembedding immunogold labelling for electron microscopy on ultrathin sections of apical and basal turns of the guinea-pig cochlea with anticalbindin (Swant), followed by appropriated gold conjugated secondary antibodies. This technique allows quantitative analysis of the distribution of labelling by counting gold particle densities. RESULTS: Outer hair cells in the apical turn were significantly more heavily labelled than those in the base (P < 0. 001). In addition, at the apex there was a progressive reduction across the three rows of outer hair cells towards the modiolus (P < 0.005) although at the base no radial gradient was detected. CONCLUSIONS: These results confirm previous reports of gradients of calbindin distribution in the organ of Corti. This distribution corresponds with the pattern of hair cell loss that occurs, e.g. after some forms of ototoxicity and it may therefore contribute to the diffential susceptibility of hair cells to damage. ACKNOWLEDGEMENT: This work was supported by the Wellcome Trust.