Table I.

Directly measured plasma membrane electrical potentials (ΔΨ) and direction of energy requiring flux, as determined by the Nernst and Ussing-Teorell equation

External concentrations of NH₄⁺ and NO₃⁻ were 10 mm. Membrane potentials are the means ± sd of seven to 38 replicates. Cytosolic activity estimates used in the calculations were found using both elution and subsampling protocols; the direction of the energy-requiring flux was the same regardless of protocol.

N Treatment	[K+]ext	ΔΨ	Energy-Requiring Flux
	mm	mV
NH4+	0.1	−118 ± 10	Influx
	1.5	−123 ± 18	Efflux
	5	−119 ± 9	Efflux
	20	−59 ± 6	Efflux
	40	−51 ± 9	Efflux
NO3−	0.1	−141 ± 11	Influx
	1.5	−125 ± 12	Efflux
	5	−119 ± 13	Efflux
	20	−86 ± 17	Efflux
	40	−86 ± 10	Efflux