Table 1. Rb uptake by the Na,K-ATPase in quiescent mouse EDL muscle measured by ICP-MS using equimolar replacement of RbCl for KCl in the uptake buffer.

	Normalized to wet weight			Normalized to S-based mass
	Rb content ng/g	RSD %	Rb transport rate nMol Rb/g-min	Rb content ng/g	RSD %	Rb transport rate nMol Rb/g-min
no ouabain (n = 10)	397,135.9 ± 142,548.5	35.9	467.2	459,860.8 ± 36,809.4	8.0	541.0
+ouabain (n = 5)	123,431.5 ± 23,393.8	19.0	145.2	120,601.2 ± 6,239.8	5.2	141.9
NET transport by Na,K-ATPase			322.0			399.1

Rb transport rate was measured using a 10 min incubation in physiological saline containing 4.7 mM RbCl in place of KCl, and nominally 0 mM KCl, at 32 °C. Non-specific Rb uptake contributed by all other K and Rb transport pathways was measured in independent muscles using 1 mM ouabain. Using S-based muscle mass, non-specific Rb uptake was 26.2% of total uptake, and was subtracted to obtain net ouabain-sensitive uptake by the Na,K-ATPase. RSD, relative standard deviation. Rb content was normalized either to weighed wet tissue mass or to the S-based mass.