In five different secondary monolayer cultures of rabbit articular chondrocytes, 72-89% of the collagen synthesized was Type I, as determined by a chain separation and CNBr-cleavage peptide analysis. When sister cells were transferred to spinner bottles after primary monolayer culture growth, 88% of the collagen formed in four separate experiments was Type 11. A reversion to Type I collagen synthesis occurred when the spinnercultured cells were returned to monolayer flasks. The change in the species of collagen depended on the suspension condition and not on the low CaZ+ content (0.33 mM) of the spinner medium. These findings parallel the switch to phenotypic glycosaminoglycan synthesis that also occurs when monolayer-cultured cells are transferred to spinner bottles. Whether this phenomenon arises through a genetic control mechanism rather than environmental selection for particular cohorts of cells has not yet been determined. In monolayer culture, lapine articular chondrocytes have been shown to display two major differences from normal cartilage in the matrix components produced: a) an apparent shift of collagen synthesis from tissue-specific Type I1 to Type I ( I ) ; and b) large changes in the amount and profile of glycosaminoglycan (GAG) species (2). In a recent study, however, it was shown that transfer of monolayered-cultured chondrocytes to suspension conditions resulted in a dramatic return of chondroid expression of GAGS (2). The following study demonstrates an analogous phenomenon with respect to the types of collagen formed in cultures from a common cell inoculum: In monolayers, the collagen is primarily Type I, whereas in spinner bottles, the bulk is Type I I . MATERIALS AND METHODSSeven separate cultures of lapine articular chondrocytes were studied.Media and Reagents. These materials were acquired from the following commercial suppliers. Ham's Nutrient F-12, minimal Eagle's (MEM), minimal Eagle's for spinner culture (SMEM), Dulbecco-Vogt (DMEM), and a modification of the latter for spinner conditions (SDMEM) (see below) were from Grand Island Biological Co. Fetal Calf Serum (FCS) came from Associated Biomedic Sytems. CM-cellulose (CMC, Whatman CM32) and DEAE-cellulose (DEAE. Whatman DE 52) were acquired from H. Reeve Angel. BioGel P-2 was from BioRad Laboratories, and CNBr from Eastman Organic Chemicals. SH-2-Glycine (9.4 Ci/mM ) and Liquifluor came from the New England Nuclear Corp. Pepsin (PM), collagenase (CLS), testicular hyaluronidase (HSE), and trypsin (TRL) were purchased from Worthington Biochemical

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