EXTRACELLULAR-MATRIX AND PULMONARY-HYPERTENSION - CONTROL OF VASCULARSMOOTH-MUSCLE CELL CONTRACTILITY

Pulmonary hypertension is characterized by increased vascular resistan ce due to smooth muscle cell hyperactivity and excess deposition of ex tracellular matrix (ECM) in the vessel wall. We investigated the possi bility that changes in cell-ECM interactions may play an active role i n this process by modifying the contractile response of pulmonary vasc ular smooth muscle (PVSM) cells. Contractility was measured within ind ividual cultured PVSM cells, when resting or stimulated with vasoactiv e agents, by quantitating changes in stiffness of the cytoskeleton (CS K) using magnetic twisting cytometry (N. Wang, J. P. Butler, and D. E. Ingber. Science 260: 1124-1127, 1993). Control studies confirmed that changes in CSK stiffness closely paralleled alterations in cell contr action and relaxation as measured in response to endothelin-1 (ET-1) a nd dibutyryl guanosine 3',5'-cyclic monophosphate (cGMP), respectively , in a collagen gel contraction assay. CSK stiffness and contractile t one in cultured PVSM cells increased in direct proportion as the densi ty of fibronectin (FN) coating was raised from 10 to 500 ng/well in 96 -well plates. Dibutyryl cGMP had no effect in cells on low FN, althoug h it completely inhibited the FN-dependent increase in CSK stiffness o n higher ECM densities. In contrast, ET-1 induced the greatest increas e in CSK stiffness on the intermediate FN density (100 ng/well). The r educed sensitivity to ET-1 on high FN was not due to dysfunction of th e contractile apparatus nor to changes in protein tyrosine phosphoryla tion. Taken together, these results show that ECM can modulate PVSM ce ll contractility and suggest that the changes in ECM observed in hyper tensive vessels could play an important role in the etiology of this d isease.