Organized channels allow vertebrates to make muscles more efficient.
Vertebrates use two different systems for controlling muscle contraction, with DHPR calcium channels acting as voltage sensors in both. In skeletal muscle, tetrads of DHPR proteins associate directly with ryanodine receptors (RyRs). In response to electrical stimulation, DHPRs directly signal RyRs, causing release of internal stores of calcium and muscle contraction. By contrast, DHPR and RyR in cardiac muscle are located near one another in adjoining membranes but do not interact directly. For DHPR to activate RyR, the channel must allow a flood of extracellular calcium into the cell. All invertebrate muscles use this latter system.
Using structural analysis of muscle samples from four species that characterize the vertebrate–invertebrate evolutionary junction,...
