Cameron Hill
@cameronhill13.bsky.social
Postdoc in muscle biophysics at KCL using X-ray diffraction to observe regulation of contraction in skeletal muscle. Interests in ageing, obesity and exercise phys.
Excited to share our preprint using time-resolved small-angle X-ray diffraction to study myosin motor conformations during isometric twitch and tetanus contractions in the slow-twitch rat soleus skeletal muscle #myoblue
October 15, 2025 at 12:55 AM
Excited to share our preprint using time-resolved small-angle X-ray diffraction to study myosin motor conformations during isometric twitch and tetanus contractions in the slow-twitch rat soleus skeletal muscle #myoblue
When examining sarcomere length, SL remains constant during the first isometric phase of relaxation (blue). When force starts to decline, weak sarcomeres being to yield and stretch as identified by two populations of sarcomeres, eventually resulting in exponential force decay.
March 13, 2025 at 1:06 PM
When examining sarcomere length, SL remains constant during the first isometric phase of relaxation (blue). When force starts to decline, weak sarcomeres being to yield and stretch as identified by two populations of sarcomeres, eventually resulting in exponential force decay.
In this period called "isometric relaxation" motors begin to detach as signalled by a decrease in the equatorial intensity ratio as myosin moves away from actin (blue), meaning the strain per attached motor increases.
March 13, 2025 at 1:06 PM
In this period called "isometric relaxation" motors begin to detach as signalled by a decrease in the equatorial intensity ratio as myosin moves away from actin (blue), meaning the strain per attached motor increases.
IAL2 increases as motors attach to actin and tropomyosin moves into the actin grooves. When load is removed and myosin detaches, IAL2 ↓ despite the high Ca2+ as tropomyosin is allowed to move out of the grooves between actin. When Ca2+ ↓, the change in IAL2 is similar to force.
March 13, 2025 at 1:06 PM
IAL2 increases as motors attach to actin and tropomyosin moves into the actin grooves. When load is removed and myosin detaches, IAL2 ↓ despite the high Ca2+ as tropomyosin is allowed to move out of the grooves between actin. When Ca2+ ↓, the change in IAL2 is similar to force.
When load is removed (grey shade) the thick filament begins to switch off as motors detach, and occurs much faster than force due to the small number of motors required to drive shortening. When Ca2+ is removed IML1 remains low (blue shade) and slowly returns to its OFF state.
March 13, 2025 at 1:06 PM
When load is removed (grey shade) the thick filament begins to switch off as motors detach, and occurs much faster than force due to the small number of motors required to drive shortening. When Ca2+ is removed IML1 remains low (blue shade) and slowly returns to its OFF state.
X-ray diffraction patterns were collected and reflections ascribed to certain sarcomere structures. (See ALT text for description of each reflection examined). I want to draw attention to two reflections in particular - the ML1 and AL2 reflections.
March 13, 2025 at 1:06 PM
X-ray diffraction patterns were collected and reflections ascribed to certain sarcomere structures. (See ALT text for description of each reflection examined). I want to draw attention to two reflections in particular - the ML1 and AL2 reflections.
To test this, we visited ID02 at
@esrf.fr to perform time-resolved X-ray diffraction on mouse EDL muscles. To separate out the contribution of load and [Ca2+]i we imposed ramp shortening to remove load when [Ca2+]i was high, and by allowing reuptake of Ca2+ by the SR.
@esrf.fr to perform time-resolved X-ray diffraction on mouse EDL muscles. To separate out the contribution of load and [Ca2+]i we imposed ramp shortening to remove load when [Ca2+]i was high, and by allowing reuptake of Ca2+ by the SR.
March 13, 2025 at 1:06 PM
To test this, we visited ID02 at
@esrf.fr to perform time-resolved X-ray diffraction on mouse EDL muscles. To separate out the contribution of load and [Ca2+]i we imposed ramp shortening to remove load when [Ca2+]i was high, and by allowing reuptake of Ca2+ by the SR.
@esrf.fr to perform time-resolved X-ray diffraction on mouse EDL muscles. To separate out the contribution of load and [Ca2+]i we imposed ramp shortening to remove load when [Ca2+]i was high, and by allowing reuptake of Ca2+ by the SR.
When [Ca2+]i increases on electrical stimulation, troponin becomes saturated with Ca2+ triggering a movement of troponin and tropomyosin exposing binding sites. Motors then leave their helical tracks in a load-dependent manner. High load + mechanosensing = rapid activation.
March 13, 2025 at 1:06 PM
When [Ca2+]i increases on electrical stimulation, troponin becomes saturated with Ca2+ triggering a movement of troponin and tropomyosin exposing binding sites. Motors then leave their helical tracks in a load-dependent manner. High load + mechanosensing = rapid activation.
In resting muscle myosin motors in the thick filaments are arranged in an OFF state unavailable for actin binding, with a tiny fraction of sentinel motors. Troponin and tropomyosin in the actin-containing thin filaments are also OFF at low [Ca2+]i, preventing myosin binding.
March 13, 2025 at 1:06 PM
In resting muscle myosin motors in the thick filaments are arranged in an OFF state unavailable for actin binding, with a tiny fraction of sentinel motors. Troponin and tropomyosin in the actin-containing thin filaments are also OFF at low [Ca2+]i, preventing myosin binding.