. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SODIUM CHANNELS IN SQUID MUSCLE FIBERS 339. Na 13 [nS/pF] 6 o 00 5 D 4 O 3 o 9 - * 0 r XX«OD o 0 2 4 6 8 fiber diameter [| 10 Figure 3. Correlation of Na channel expression and muscle fiber type. All data were derived as in Fig. 2. (A-C) Video prints of three different muscle cells taken shortly after achieving the whole-cell con- figuration and records of membrane current at 0 mV attained after contraclure (inset in Fig. 3C). Currents in Fig. 3A are shown with and without a prepulse to inactivate /Na. /Na was not detectable
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SODIUM CHANNELS IN SQUID MUSCLE FIBERS 339. Na 13 [nS/pF] 6 o 00 5 D 4 O 3 o 9 - * 0 r XX«OD o 0 2 4 6 8 fiber diameter [| 10 Figure 3. Correlation of Na channel expression and muscle fiber type. All data were derived as in Fig. 2. (A-C) Video prints of three different muscle cells taken shortly after achieving the whole-cell con- figuration and records of membrane current at 0 mV attained after contraclure (inset in Fig. 3C). Currents in Fig. 3A are shown with and without a prepulse to inactivate /Na. /Na was not detectable in the fibers shown in panels B or C (for all current traces, vertical scalebar = 125 pA/pF. horizontal scalebar = 5 ms). (D) Specific Na conductance (GNa; derived as described in text) is shown plotted versus muscle cell diame- ter and type (see text for details). Diameter measurements were made from digitized video frames using image analysis software (NIH-lmage ). and mean diameter was calculated from 10 measurements equally spaced along the length of the fiber. 7Na - r relation, and these values were normalized by input capacity (<7Na; nS/pF). These data are plotted ver- sus diameter in Fig. 3D for fibers 120 ^m (O) in length, and for multipolar-cell arms (X). The approximate thickness of the mantle musculature is 120 nm (equal to the length of radial muscle fibers) in a squid of the size used for the dissociations (unpub. data). Fibers longer than this value are thus likely to be derived from circular muscle. Seven out of eight fibers showing significant GNa lie in the 2-5 ^m range, and most of these are > 120 nm long. All fibers lacking GNa are >4 ^m di- ameter, and half of these are > 120 /urn long. Thus, on the basis of the level of G^a, we conclude that two classes of circular muscle fibers exist, and there appear to be two corresponding size classes. Presumably the small, Na-channel-rich fibers are central circular fi- bers ( ± jim diameter,
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
