Calcium movement in cardiac muscle
Dirk Gillespie (Molecular Biophysics and Physiology, Rush University Medical Center)
(February 25, 2013 3:00 PM - 3:50 PM)
Heart muscle starts to contract when Ca2+ released from the sarcoplasmic reticulum (SR) binds to contractile proteins. The Ca2+ is released from the SR (a Ca2+ storage organelle) through calcium-selective ion channels called ryanodine receptors (RyRs). RyRs are activated (opened) by changes in cytosolic Ca2+ concentrations. Therefore, when some RyRs open to release Ca2+, neighboring RyRs are activated to release even more Ca2+ in a process called calcium-induced calcium release (CICR). Experiments suggest that this positive-feedback process does, however, terminate long before the SR is depleted of Ca2+, but how is not currently understood.
Several aspects of this Ca2+ movement will be discussed from the point of view of physics and mathematics. These include how RyRs select and efficiently conduct Ca2+ for sustained release, how probability theory can help us understand CICR, and how the physics of phase transitions might explain CICR initiation and, more importantly, its termination before the SR is deleted of Ca2+.