Many marine invertebrates, such as squid, have extracellular fluids that resemble seawater and therefore have much higher intracellular ion concentrations than mammals. For a squid neuron, the ionic concentrations are roughly
$$\begin{array}{lrr}
& \text { intracellular } & \text { extracellular } \\
\text { ion } & \text { conccritration } & \text { concentration } \\
\mathrm{K}^{+} & 350 \mathrm{mM} & 10 \mathrm{mM} \\
\mathrm{Na}^{+} & 40 \mathrm{mM} & 440 \mathrm{mM} \\
\mathrm{Cl}^{-} & 100 \mathrm{mM} & 560 \mathrm{mM} \\
\mathrm{Ca}^{2+} & 2 \times 10^{-4} \mathrm{mM} & 10 \mathrm{mM} \\
\mathrm{pH} & 7.6 & 8.0
\end{array}$$
If the resting potential of the plasma membrane, $V_{m},$ is $-70 \mathrm{mV}$ are any of the ions at equilibrium? How far out of equilibrium, in $\mathrm{mV}$, is each ion? What is the direction of net movement of each ion through an open channel permeable to that ion?