Morphology and Transverse Stiffness of Drosophila Myofibrils Measured by Atomic Force Microscopy

• Published in: Biophysical journal Vol. 78; no. 3; pp. 1490 - 1497
• Main Authors: Nyland, Lori R., Maughan, David W.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-03-2000; Biophysical Society
• Subjects: Animals; Drosophila; Drosophila melanogaster; flight muscles; Flight, Animal; Glass; Image Processing, Computer-Assisted; indirect flight muscle; Insects; Microscopy, Atomic Force - methods; Models, Biological; Molecular biology; Muscle Fibers, Skeletal - physiology; Muscle Fibers, Skeletal - ultrastructure; muscle physiology; Muscle, Skeletal - physiology; Muscle, Skeletal - ultrastructure; Muscular system; Myofibrils - physiology; Myofibrils - ultrastructure; Scientific imaging
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(00)76702-6

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
⊥
) 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
⊥
) was 94
±
41 kPa in the rigor state and 40
±
17 kPa in the relaxed state. The value of
E
⊥
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.