PROTEOGLYCAN SYNTHESIS BY SCLERAL CHONDROCYTES IS MODULATED BY A VISION DEPENDENT MECHANISM

Proteoglycan synthesis was measured in chick sclera at the onset of form-deprivation myopia, as well as in the period immediately following removal of the occluder. Two day-old chicks were monocularly form vision deprived for periods from one to ten days and proteoglycan synthesis was determined after placing posterior scleral buttons in organ culture and measuring (SO4)-S-35 incorporation into glycosaminoglycans. Following 24 hrs of form-deprivation, proteoglycan synthesis was 33% higher in myopic eyes as compared with paired control eyes. The rate of proteoglycan synthesis further increased to levels 83% higher than controls after four days of form-deprivation and remained elevated throughout the ten day period of deprivation. Removal of the occluder after 10 days of form-deprivation resulted in a rapid drop in the rate of proteoglycan synthesis to control levels within 24 hrs. Proteoglycan synthesis was also measured in scleral chondrocytes isolated from control and myopic eyes after 10 days of form-deprivation. Proteoglycan synthesis by chondrocytes from myopic eyes did not return to control levels until 48 hrs after plating. Since the rate of proteoglycan synthesis returns to control levels more quickly during the recovery period ex vivo than when scleral chondrocytes from myopic eyes are placed in cell culture, we suggest that a mechanism is present within the eye which rapidly lowers the rate of proteoglycan synthesis in response to form vision.