MECHANICAL CHANGES AFTER HISTAMINE ACTIVATION OF INTACT SINGLE VASCULAR SMOOTH-MUSCLE CELLS

Although several different models have been proposed to explain force maintenance in vascular smooth muscle, the molecular mechanism respons ible for this phase of contraction has yet to be elucidated. To invest igate the molecular mechanism for force maintenance, force and stiffne ss were measured during (1 mu M histamine) activation of single intact arterial smooth muscle cells, After histamine stimulation, the rise i n quadrature stiffness preceded force (P < 0.05) and reached a steady state plateau before force (P < 0.05), These data suggest that the num ber of cycling crossbridges increases during force activation and then remains constant during force maintenance, In-phase stiffness, on the other hand, continued to increase in amplitude after force had reache d a steady state, The increase in the in-phase stiffness during force maintenance suggests that during force maintenance either a population of cross-bridges in an attached nonforce producing state develop or n oncross-bridge force bearing structures are formed. (C) 1996 Academic Press, Inc.