Nature of the inhibitory effect of collagenase on phosphodiesterase activity

The level of phosphodiesterase (PDE) activity is lower in collagenase-isolated human fat cells than in adipose tissue fragments. The inhibition is not species-specific since collagenase also inhibits PDE in rat adipose tissue and bovine heart. In subcellular fractions from isolated fat cells, the PDE activities were lowest in the plasma membrane-enriched fractions and highest in the cytosolic fractions. This is opposite to PDE in subcellular fractions obtained from adipose tissue fragments. In dose-response experiments, collagenase inhibited particulate PDE to a much larger extent than it inhibited soluble PDE. The extracellular activities of PDE were completely eliminated by collagenase. Repeated washings or reincubation of the isolated fat cells did not restore the PDE activity. A purified collagenase with low specific protease activity reduced the PDE activity in isolated fat cells to a lesser extent than did a collagenase with high specific protease activities. Collagen and several protease inhibitors were ineffective in preventing the reduction of PDE after exposure to collagenase. It is concluded that nonspecific proteases in the collagenase preparations used for fat cell isolation interact with particulate and soluble PDE causing an irreversible inhibition of PDE activity in isolated fat cells. Of the various forms of PDE, plasma membrane-associated PDE seems most sensitive to collagenase.