REGULATION OF UREASE LEVELS IN MICROCOSM DENTAL PLAQUE

The regulation of plaque urease activity by urea, ammonia and arginine was examined using microcosm dental plaques cultured in a multi-plaqu e 'artificial mouth' from the mixed oral microbiota. The plaques were supplied periodically with sucrose and continuously (3.6 ml/h/plaque) with a mucin containing medium (BMM) supplemented either with urea at concentrations found in saliva, or with arginine, or ammonia. Urease l evels in plaque range from 400 to 1500 nmol NH3/min/mg plaque protein. In the absence of urea supplementation, microcosm plaque urease level s were usually less than 100 nmol NH3/min/mg protein. They decreased a fter 2 to 3 wks growth and were not restored by subsequent urea applic ation. BMM containing 1, 5 and 20 mmol/l urea throughout growth produc ed a proportional increase in urease levels initially, similar to thos e observed in plaques in vivo. Subsequently, urease levels decreased a s the plaques aged. BMM supplemented with arginine (1 mmol/l) or ammon ia (2 mmol/l) reduced urease levels. The high urease levels found in s upragingival plaque can be explained by the availability of urea at co ncentrations secreted in saliva. Ammonia and arginine lowered plaque u rease levels.