. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 338 W. F. GILLY ET AL B+C. Figure 1. Non-giant and giant motor axons contribute approxi- mately equally and additively to the twitch of circular muscle fibers. The nerve-muscle preparation consisted ot a stellate ganglion from a juvenile Loligo opalescens connected by stellar nerves to a sector of mantle cut parallel to the circular muscle bands and attached to a force transducer (BG-IOGM, Kulite Inc., Leonia, NJ). Motor axon stimula- tion was effected with a coaxial, bipolar electrode. (A) A single 3 V shock excited only no
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 338 W. F. GILLY ET AL B+C. Figure 1. Non-giant and giant motor axons contribute approxi- mately equally and additively to the twitch of circular muscle fibers. The nerve-muscle preparation consisted ot a stellate ganglion from a juvenile Loligo opalescens connected by stellar nerves to a sector of mantle cut parallel to the circular muscle bands and attached to a force transducer (BG-IOGM, Kulite Inc., Leonia, NJ). Motor axon stimula- tion was effected with a coaxial, bipolar electrode. (A) A single 3 V shock excited only non-giant motor axons. (B) A single 5V shock ex- ceeded threshold for giant axon excitation. (C) Summed response due to stimulation of non-giant motor axons with five 3V shocks at 50 Hz. (D) Superposition of the records in panels B and C along with their algebraic summation (B + C, dotted trace) is compared with the re- sponses to five 5V shocks at 50 Hz which excite giant and non-giant motor systems. External solution was artificial seawater. 7= 16°C. and including those characteristic of escape jetting (9). Third, giant and non-giant axon-driven responses can contribute nearly equally to escape jetting (6). As a first step towards definition of the relevant neuro- muscular relationships in squid muscle, we have at- tempted to identify a muscle fiber type with electrical properties suggestive of all-or-none excitability, and which therefore is likely to be associated with the giant axon system. Whole-cell voltage clamp recordings from dissociated mantle muscle fibers were carried out using a Na-containing internal solution that blocks K channels (10). Figure 2A illustrates a muscle fiber shortly after achieving the whole-cell configuration and after repeti- tive pulsing (inset), which caused irreversible contrac- ture. This phenomenon reliably yielded well-clamped cells, and all data in this paper were similarly obtained. Transient inward current recorded from this muscle fi- b
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