Table I.

Effects of 10⁻⁶ M TTX on ²²Na uptake in soleus muscles from WT and mutant mice

Genotype	22Na uptake	Significance of difference between controls and TTX (p-value)
	nmol/g wet wt/min
WT	242 ± 6 (8)	<0.012
WT + TTX	213 ± 8 (8)
Mutant	403 ± 13 (8)	<0.001
Mutant + TTX	231 ± 11 (8)

Soleus muscles were prepared from 12-wk-old mice and mounted on electrodes at resting length, equilibrated for 30 min in KR buffer at 30°C, transferred to tubes containing 0.5 µCi/ml ²²Na, and incubated for 5 min. To remove ²²Na from the extracellular space, all muscles were washed twice for 5 min in KR at 30°C, blotted, weighed, and taken for counting. 10⁻⁶ M TTX, when added, was present during the last 15 min of the equilibration period. The uptake of ²²Na was calculated from the specific activity of the isotope in the incubation medium. Results are expressed as nanomoles of ²²Na/gram of wet weight/minute ± SEM in soleus of WT and mutants and their contralateral muscles exposed to TTX. The number of muscles is given in parentheses.