POLARIZED FT-IR MICROSCOPY OF CALCIFIED TURKEY LEG TENDON

Polarized Fourier transform infrared microscopy (FT-IRM) was used to a ssess the orientation of mineral and matrix components of the normally calcified turkey leg tendon. Two groups of tendon, <16 weeks of age ( young) and >60 weeks of age (old), were analyzed, Linear sequences fro m calcified, non-calcified, and transitional regions of the tendons we re examined. Spectra collected in the ''parallel polarization'' mode w ere acquired with the electric vector of the infrared radiation parall el to the collagen fiber axis whereas spectra collected in the ''perpe ndicular polarization'' mode were acquired with the electric vector of the infrared radiation perpendicular to this axis. The nu(2) carbonat e (850-890 cm(-1)) and nu(1), nu(3) phosphate (900-1180 cm(-1)) contou rs of the tendon mineral as well as the collagen amide I, II, and III bands of the extracellular matrix all displayed marked dichroism. The CO32- ions substituted for PO43- (878 cm(-1), type B substitution) in the tendon mineral displayed parallel dichroism while the CO32- ions s ubstituted for OH (871 cm(-1), type A substitution) in the tendon mine ral displayed perpendicular dichroism. These orientational effects for both sites of carbonate substitution were greater in the older animal s. The polarization properties of the nu(1), nu(3) phosphate contour w ere analyzed by use of an empirical anisotropy parameter (A), the valu e of which monitors the degree of orientation. This index significantl y increased in the other animals indicating that aging produces a more highly oriented mineral. The amide I, II, and III contours of the col lagen extracellular matrix also exhibited marked dichroism, The amide I component exhibits perpendicular dichroism while the amide II and II I components exhibit parallel dichroism. The current study demonstrate s the ability of polarized FT-IRM to assess the orientation of the min eral and matrix components of calcified tissue at the microscopic leve l.