Electromechanical coupling in a molluscan muscle, the radula protractor of Busycon canaliculatum

Abstract

The radula protractor can be made to be spontaneously rhythmic, although it is normally a quiescent, phasic muscle, with apparently multi-unit organization. Acetylcholine and potassium depolarize with contracture. Once a radula muscle has been put into a long-lasting contracture by acetylcholine, tryptamine can repolarize it with accompanying relaxation. In the continued presence of acetylcholine and tryptamine, the repolarization and relaxation gradually taper off while membrane oscillation accompanied by mechanical rhythmicity develops. Contrariwise, if a radula protractor is in a potassium contracture, tryptamine will potentiate the contracture without affecting the level of membrane depolarization. Potentiation of potassium contracture, without changing potential level, can also be effected by increased calcium concentrations or by caffeine. After a muscle has been soaked in artscial sea water lacking calcium, its twitch tension, tetanic tension, potassium contracture, and acetylcholine contracture become directly dependent on external calcium concentration.

Physiological properties of the penis retractor muscle of Aplysia

“…Peak depolarizations (summated ejps) were achieved a t frequencies between 30 and 50 Hz (cf. Hill et al, 1970;Kobayashi, 1972;Ozeki, 1962), and peak tensions were reached at even lower frequencies. Contractile responses of the muscle were slow in developing and long in duration with time courses of seconds.…”

“…Some molluscan muscle, however, does display a "spike-like" response, usually less than 20 mV in amplitude. Such responses have been reported to occur when the muscle fibers are depolarized, as by increased [K+]o (Burnstock et al, 1967;Hill et al, 1970) or by repetitive nerve stimulation (Hill et al, 1970;Kobayashi, 1972). It is possible that some portion of the large fast ejps with initially rapid repolarizations in the penis retractor muscle (Fig.…”

Excitatory effects of cholinergic, adrenergic and glutaminergic agonists on a buccal muscle of Aplysia

“…On occasion, muscles displayed recurrent contractions of varying amplitude and intervals in the normal bathing solutions. Endogenous contractile activity has also been observed in a variety of other molluscan buccal muscles under various experimental conditions (Fange and Mattison, 1958;Feder and Lasker, 1968;Hill, Greenberg, Irisawa and Nomura, 1970;Kobayashi, 1974). In the present investigation, such contractions could either begin after a time or be present from the onset of the experiment and subsequently stop.…”

Functional anatomy of the sperm storage organs in Pulmonata: the simple spermatheca of Bradybaena fruticum (Gastropoda, Stylommatophora)

“…The endurance cannot be high because mitochondria are not abundant (Josephson 1975;Plesch 1977a;Nicaise and Amsellem 1983). The quite extensively developed tubular and caveolar system formed by invaginations of the sarcolemma and the sarcoplasmic reticulum, providing calcium (Hill et al 1970;Heyer et al 1973;Hoyle 1995), indicates that the muscle cells relax rapidly, at least faster than in A. arbustorum, where this system is less complex. This and the less-ordered arrangement of myofilaments are the only differences in the fine structure of the muscle cells surrounding the spermatheca compared to A. arbustorum (Bojat et al 2001a).…”