Receptors for multiplication-stimulating activity (MSA) on rabbit chondrocytes

Multiplication-stimulating activity (125I-MSA) has been shown to bind to isolated rabbit chondrocytes, the binding being dependent on time, temperature, and cell density. Nonspecific binding was approximately 15%. Unlabelled MSA at 100 ng/ml inhibited 125I-MSA binding by 50%. Porcine insulin (0.5-10 micrograms/ml) did not compete with MSA but resulted in a 10-15% increase in 125I-MSA binding. The data suggest that normal chondrocytes carry IGF2-type receptors as well as the IGF1 type previously described.