An electron microscopic autoradiographic study of proline incorporation by mouse lingual epithelium

Summary

Mouse lingual epithelium incorporates significant amounts of L-proline-2, 3-H³ one hour after intraperitoneal injection of the tritiated amino acid. All viable cell strata incorporated approximately equal amounts of proline as assessed by autoradiographic techniques. Grain counts at 30 minutes, 1 hour, 4 hours and 24 hours, the four time periods studied, indicated a progressive incorporation of proline up to 4 hours following injection. Preferential incorporation of proline into any one cell structure or group of structures was not observed. Keratohyalin granules (KHG's) demonstrated incorporated proline; however, usually only one silver grain appeared over each granule, and, based on grain counts, the amount of proline incorporated by KHG's appeared slightly less than the general labeling observed in KHG-containing cells. This finding supports recent biochemical studies which have indicated a considerably lower proline content of keratohyalin than had previously been reported. Significant proline incorporation into the epithelial basal lamina was not observed during the 24 hours of this study. Thus, while recent recombination experiments have conclusively demonstrated that epithelial basal cells synthesize considerable quantities of basal lamina in a 24 hour period; it would appear that epithelial basal cells contribute little to a formed, intact basal lamina. This finding lends credence to the concept of a long basal lamina turnover time.