Alterations in cyclic AMP phosphodiesterase activities during differentiation of 3T3-L1 cells

3T3-L1 cells contain multiple forms of cyclic nucleotide phosphodiesterase in both supernatant (100,000 X g, 40 min) and particulate fractions. Supernatant fractions from both undifferentiated and differentiated cells contained calmodulin-sensitive activity. In undifferentiated 3T3-L1 cells, only a small fraction of the total cAMP phosphodiesterase activity was found in the particulate fraction and the specific activity of the particulate was lower than the supernatant. With differentiation the specific activity of the particulate doubled, and there was a dramatic increase in total activity in this fraction, while in the supernatant total cAMP phosphodiesterase activity increased less and specific activity decreased. The particulate fraction accounted for approximately 70% of the total cAMP phosphodiesterase activity in differentiated cells in contrast to about one-third in undifferentiated cells. In addition, there was a qualitative change in particulate phosphodiesterase activity. In fractions from 3T3-L1 adipocytes, with either cAMP or cGMP as substrate, Lineweaver-Burk plots were nonlinear, with low Km components of less than 1 microM, and cGMP inhibited cAMP hydrolysis. In particulate fractions from undifferentiated cells, cGMP did not inhibit and often enhanced hydrolysis of cAMP. With differentiation, there was also a marked increase in particulate cGMP phosphodiesterase activity. cAMP and cGMP phosphodiesterase activities solubilized from particulate fraction of differentiated cells coeluted from DEAE-Biogel and exhibited kinetic properties similar to the crude particulate fractions. During differentiation, there seems to be an alteration in the distribution of phosphodiesterase activity as well as the appearance of a particulate phosphodiesterase with kinetic properties similar to a particulate phosphodiesterase found in mature rat adipocytes.