Two types of striated muscle suggest two‐geared swimming in the pteropod mollusc Clione limacina

• Published in: Journal of Experimental Zoology
• Main Authors: Satterlie, Richard A., Goslow, G. E., Reyes, Arjun
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1990
• Subjects: Clione limacina
• Online Access: http://dx.doi.org/10.1002/jez.1402550202; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fjez.1402550202; https://onlinelibrary.wiley.com/doi/pdf/10.1002/jez.1402550202

Abstract Forward locomotion in the pteropod mollusc Clione limacina occurs in two distinct speeds, slow and fast. Fast swimming can include an initial ballistic escape phase following proper stimulation. Escape swimming is always followed by a period of fast swimming (both are forms of fast swimming), but changes from slow to fast swimming can occur without activation of the escape phase. Light and electron microscopical examination of the swim musculature reveals two types of striated muscles, suggesting that the neuromuscular system is designed to operate with two distinct “gears”. Histochemical staining for myosin ATPase (alkaline preincubation) and NADH diaphorase suggests that swim musculature includes slow‐twitch, fatigue‐resistant fibers and fast‐twitch fatigable fibers. Combined electrophysiological and force transducer recordings support the twitch speed dichotomy, as fast‐twitch motor units were found to have twitch times of 20 ms (time to peak tension) while slow‐twitch motor unit twitch times were found to be more than three times as long. Fatigue tests were used to simulate both slow and fast swimming. Fatigue rates during simulated fast swimming suggest that the change from escape swimming to fast swimming may be partly explained by fatigue in the fast‐twitch motor units, but other factors, possibly including peripheral modulation of muscle activity, must also contribute to the change.