Iodoplatinate visualization of phospholipids in rat incisor predentine and dentine, compared with malachite green...

The iodoplatinate (IP) reaction, a selective method for visualization of phospholipids, was applied to the predentine and dentine of rat incisors and compared with malachite green aldehyde (MG) fixation/staining. Spot tests indicated (1) that IP specifically stains phospholipids, but not amino acids, displaying as do phospholipids, quaternary ammonium groups; and (2) phosphatidylserine and sphingomyelin were also stained by MGA. Although this reagent is known to interact with phosphorus, phosphoproteins remained unstained. In the rat incisor, an IP-positive network including granules and thin filaments was seen in predentine 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 samples were treated either with chloroform/methanol or phospholipase C prior to the IP reaction. Pretreatment of the samples with hyaluronidase promoted subsequent diffusion of the staining. A very similar staining pattern was observed with MGA, in accordance with earlier reports. The present findings validate the histochemical results reported previously on the distribution and potential role(s) of phospholipids in dentine biomineralization.