Contractlity in Spirostomum provides for nonelectrogenic calcium regulation through energy-dissipative metabolic processes in the absence of membrane excitability

ATTEMPTS to carry out in vivo pharmacological analyses of the events leading to contraction in fast acting muscle systems have been hampered by problems due to, for example, intracellular diffusion, cell-cell interactions and extracellular control mechanisms, which arise in part because of the multicellular organisation of many vertebrate muscle systems. Their effect is to impede accurate measurement of rapid changes in the physiological and ultrastructural states throughout the system in response to specific stimuli. The most troublesome aspects of these problems can be bypassed through the use of single-celled models which have the same properties of excitability as do muscle systems.