Rapid small-angle X-ray diffraction of a tonically contracting molluscan smooth muscle recorded with imaging plates

Small-angle X-ray diffraction patterns from the anterior byssus retractor muscles of Mytilus edulis contracting tonically in response to stimulation with acetylcholine were recorded in a 30 s exposure with synchrotron radiation and a high-sensitivity X-ray area detector called an imaging plate. The 190 Å layer line from the thin filaments increased in intensity with increase in tonic tension up to 6 x 10⁴ kg m^-2. Above this value, the layer-line intensity remained almost constant and comparable to that for a contracting skeletal muscle, indicating that the same structural changes of the thin filaments occur in both muscles.