Abstract
Ionic mechanisms of the action potential of longitudinal flight muscle fiber were studied in the fly,Sarcophaga bullata. Depolarization of the fiber membrane initiates the fast spikes which may be followed by a plateau response. The fast spike is a graded response in normal saline, but is converted to an all-or-none response in TEA solutions. It is eliminated in Ca-free media, suppressed by 12 mM Co++, and the overshoot increases with an increasing Ca++ concentration. Both the spikes and the plateau are TTX insensitive. Although the fast spike is produced in Na-free media, the rate of rise and overshoot of the spike are reduced. However, Na+ will not support spikes in the absence of Ca++. Plateau responses in normal saline are about 12 s in duration with a potential level of about −25 mV. Both the plateau potential and duration increase with an increasing Na+concentration, and the plateaus are eliminated in Na-free media.
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