title: Morphology and transverse stiffness of Drosophila myofibrils measured by atomic force microscopy.
abstract: Atomic force microscopy was used to investigate the surface morphology and transverse stiffness of myofibrils from Drosophila indirect flight muscle exposed to different physiologic solutions. I- and A-bands were clearly observed, and thick filaments were resolved along the periphery of the myofibril. Interfilament spacings correlated well with estimates from previous x-ray diffraction studies. Transverse stiffness was measured by using a blunt tip to indent a small section of the myofibrillar surface in the region of myofilament overlap. At 10 nm indention, the effective transverse stiffness (K( perpendicular)) of myofibrils in rigor solution (ATP-free, pCa 4.5) was 10.3 +/- 5.0 pN nm(-1) (mean +/- SEM, n = 8); in activating solution (pCa 4.5), 5.9 +/- 3.1 pN nm(-1); and in relaxing solution (pCa 8), 4.4 +/- 2.0 pN nm(-1). The apparent transverse Young's modulus (E( perpendicular)) was 94 +/- 41 kPa in the rigor state and 40 +/- 17 kPa in the relaxed state. The value of E( perpendicular) for calcium-activated myofibrils (55 +/- 29 kPa) was approximately a tenth that of Young's modulus in the longitudinal direction, a difference that at least partly reflects the transverse flexibility of the myosin molecule.
authors.affiliation: Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont 05405, USA.
authors.forename: L R
authors.initials: LR
authors.lastname: Nyland
authors.forename: D W
authors.initials: DW
authors.lastname: Maughan
mesh_terms: D000818:Animals; D004331:Drosophila melanogaster; D005426:Flight, Animal; D005898:Glass; D007091:Image Processing, Computer-Assisted; D018625:Microscopy, Atomic Force / Q000379:methods; D008954:Models, Biological; D018485:Muscle Fibers, Skeletal / Q000502:physiology / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000502:physiology / Q000648:ultrastructure; D009210:Myofibrils / Q000502:physiology* / Q000648:ultrastructure*