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