IODOPLATINATE VISUALIZATION OF PHOSPHOLIPIDS IN RAT INCISOR PREDENTINE AND DENTIN, COMPARED WITH MALACHITE GREEN ALDEHYDE

The iodoplatinate (IP) reaction, a selective method for visualization of phospholipids, was applied to the predentine and dentine of rat inc isors and compared with malachite green aldehyde (MG) fixation/stainin g. Spot tests indicated (1) that IP specifically stains phospholipids, but not amino acids, displaying as do phospholipids, quaternary ammon ium groups; and (2) phosphatidylserine and sphingomyelin were also sta ined by MGA. Although this reagent is known to interact with phosphoru s, phosphoproteins remained unstained. In the rat incisor, an IP-posit ive network including granules and thin filaments was seen in predenti ne in the inter-collagen spaces, in many cases closely associated with collagen fibres and their periodic striations. In dentine, positively stained needle-like structures were located along individual collagen fibres, or at the surface of groups of collagen fibres. This staining pattern was unchanged on sections of material pretreated with acetone , whereas the staining was abolished or markedly reduced when the samp les were treated either with chloroform/methanol or phospholipase C pr ior to the IP reaction. Pretreatment of the samples with hyaluronidase promoted subsequent diffusion of the staining. A very similar stainin g pattern was observed with MGA, in accordance with earlier reports. T he present findings validate the histochemical results reported previo usly on the distribution and potential role(s) of phospholipids in den tine biomineralization.