Table 2.

Comparison of observed Na⁺ tracer influx, calculated net Na⁺ flux driven by 4 mV if by electrodiffusion and Na⁺ flux needed for secretion of 200 ml day⁻¹ at the blood–brain barrier

Quantity and formulae	Value (mmol kg−1 h−1)
$\begin{array}{cc}\hfill \text{Tracer influx}& =PS\times \left[{\text{Na}}^{+}\right]\hfill \\ \hfill & =70{\text{cm}}^3{\text{kg}}^{-1}{\text{h}}^{-1}\times 0.15\text{mmol}{\text{cm}}^{-3}\hfill \end{array}$	10.5
$\begin{array}{cc}\hfill \text{If}\mathrm{\Delta }V& =4\text{mV},\text{net flux}\hfill \\ \hfill & =\text{tracer influx}\times \mathrm{\Delta }V\times \left(F/RT\right)\hfill \\ \hfill & =10.5\text{mmol}{\text{kg}}^{-1}{\text{h}}^{-1}\times 4\text{mV}/27\text{mV}\hfill \end{array}$	1.55
$\begin{array}{cc}\hfill {\text{Net flux of Na}}^{+}& \text{needed for secretion of}200\text{ml}{\text{day}}^{-1}\text{in a 1}.4\text{kg brain}\hfill \\ \hfill & =0.2\text{l}{\text{day}}^{-1}\times 150\text{mmol}{\text{l}}^{-1}/(24\text{h}{\text{day}}^{-1}\times 1.4\text{kg})\hfill \end{array}$	0.9