PHARMACOLOGICAL ACTIVATION CHANGES STIFFNESS OF CULTURED HUMAN AIRWAYSMOOTH-MUSCLE CELLS

Using magnetic twisting cytometry (MTC), we measured the cytoskeletal stiffness of adherent human airway smooth muscle (HASM) cells. We hypo thesized that modulation of actin-myosin interactions by application o f contractile agonists would induce changes in cytoskeletal stiffness. In cells plated on high-density collagen, bradykinin (10(-6) M) and h istamine (10(-4) M) increased stiffness by 85 +/- 15 and 68 +/- 16%, r espectively. Increases in cell stiffness were also consistently observ ed after acetylcholine, substance P, and KCl. The bronchodilator agoni sts isoproterenol, prostaglandin E(2), forskolin, dibutryl adenosine 3 ',5'-cyclic monophosphate, and 8-bromoguanosine S',5'-cyclic monophosp hate each caused a dose-dependent decrease in cell stiffness in unstim ulated as well as bradykinin-treated cells. HASM cells plated on high- density collagen were stiffer than cells plated on low-density collage n (126 +/- 16 vs. 43 +/- 3 dyn/cm(2)) and developed more pronounced in creases in stiffness in response to bradykinin as well as more pronoun ced decreases in stiffness in response to isoproterenol. These results are consistent with the hypothesis that modulation of actin-myosin in teractions by application of contractile agonists causes changes in cy toskeletal stiffness of HASM cells. MTC may be a valuable tool for eva luating the mechanisms of pharmacomechanical coupling in ail-way smoot h muscle cells in culture.