The relation between the form of the action potential and contractions in the subumbrellar myoepithelium ofChelophyes (Coelenterata: Siphonophora)

Summary

Action potentials of the subumbrellar myoepithelium in the diphyid siphonophoreChelophyes change in form with repetitive stimulation, at first showing an increasing hump or plateau on the falling phase, and finally becoming prolonged events with a large overshoot. Simultaneous records of tension developed by the subumbrellar sheet show that this change is accompanied by increase in tension. Similar prolonged action potentials to those evoked by repetitive stimulation are seen from the outset after application of Ca⁺⁺-blocking agents such as Co⁺⁺; maximal tensions are then developed from the first stimulus. The mechanism whereby change in action potential form is linked to increased tension is discussed.