Table 4.

Determination of the g _Na/g _K ratio for I _Nab in different ionic conditions

	[K+]i = 25 mM (n = 5 cells)	[K+]i = 50 mM (n = 5 cells)	[K+]i = 130 mM (n = 2 cells)	[K+]i = 140 mM (n = 5 cells)	[K+]i = 140 mM (n = 26 cells)
[Na+]i (mM)	125	100	20	10	0.5
[Na+]o (mM)	42.1	42.1	42.1	42.1	42.1
[K+]i (mM)	25	50	130	140	140
[K+]o (mM)	2.5	2.5	2.5	2.5	2.5
E Na (mV)	−29	−23	+20	+38	+117
E K (mV)	−61	−79	−104	−106	−106
E rev for I Nab (mV)	−34.8	−34.9	−18.4	−8.1	−12.4
g Na/g K	4.50	3.70	2.23	2.12	0.72

The calculation of gNa/gK ratio indicates that INab is more permeant to Na+ than to K+ (g _Na/g _K > 1), except when the intracellular Na+ concentration is low (0.5 mM, last column, highlighted in grey). Under this experimental condition, INab becomes more permeant to K+ rather than to Na+ (g _Na/g _K < 1).