TURNOVER OF EXTRACELLULAR-MATRIX BY TYPE-II PULMONARY EPITHELIAL-CELLS

Rat type II pulmonary epithelial cells synthesize and assemble a multi component extracellular matrix (ECM) which can modulate cellular diffe rentiation in primary culture. This study defines turnover of the type II cell matrix. Turnover kinetics were analyzed in two types of pulse -chase protocols based on loss of radioactive ECM components. To estim ate turnover of previously synthesized ECM, type II cells were plated on extracted matrix that was radiolabeled 2, 3, or 6 days; alternative ly, ECM was radiolabeled in pulse-chase experiments to measure turnove r by the same cells that synthesized the matrix. Rapid initial rates o f ECM turnover were evident in both cases. While overall matrix stabil ity appeared to change with culture time, sodium dodecyl sulfate-polya crylamide gel electrophoresis analysis showed a similar spectrum of pr oteins in the ECM over the course of kinetic studies. The results reve al rapid turnover of ECM by type II cells and suggest that matrix stab ility may be regulated. These observations provide a basis for future investigations of the physiological significance of turnover of indivi dual ECM components by the alveolar epithelium.