A cardiac myosin cross-bridge has an ATPase turnover number
PHYSICS · Multi-part · Fermi University Physics · Biophysics & Medical Physics · Bioelectricity, the senses and the physics of the body · Bioelectricity, the senses and the physics of the body
Forces, Machines and Signals, Ch Muscle, heart and the fields outside the body
Problem
A cardiac myosin cross-bridge has an ATPase turnover number kcat=5.0s−1, so a single head completes one attachment-detachment cycle in a mean time τcb=1/kcat. A ventricular cell stays refractory for about 250ms of each beat, set by its calcium plateau, and its cytoplasmic calcium stays raised for roughly as long.
((a)) Find the mean cross-bridge cycle time τcb.
((b)) Estimate how many cycles one head can complete while the cell is refractory.
((c)) A student concludes that the heart relaxes between beats because each head has finished its cycle by the time the refractory period ends. Explain what is wrong with this, and state what does end each contraction and what stops successive contractions summing into a tetanus.