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Fig. 3. Isolation of Na+ currents of 4–6 d.p.f. zebrafish outer
(A) and inner (B,C) muscle. In these experiments, Na+ currents were
isolated by performing voltage-clamp recordings in saline in which all the
potassium ions were replaced by equimolar cesium ions, and all the calcium
ions replaced with equimolar cadmium ions, with BAPTA (10 mmol
l–1) supplementing the intracellular medium. (A) Stepwise, 5
ms depolarizations fail to elicit inward, Na+ currents in outer
muscle. (B,C) Stepwise, 5 ms depolarizations from a holding potential of
–90 mV to a range of potentials from –85 to +30 mV evoked rapidly
activating and rapidly inactivating, inwardly directed currents (inset), which
appeared at potentials more positive than about –40 mV and reversed
around +50 mV. Values are means ± S.E.M. of 8 experiments on
separate muscle fibres. (C) Steady state activation and inactivation of
Na+ currents recorded from inner muscle. Values are means of 12
(activation) and 9 (inactivation) separate experiments ±
S.E.M. The data thus derived for both activation and inactivation
were then fitted to a Boltzmann function giving estimated values of
V50 of activation of –7.3±1.6 mV and slope
8.4±0.5 mV/e (N=12) and V50 of
inactivation of –74.5±1.1 mV and slope of –6.0±0.2
mV/e (N=9). See text for details.
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