Normal Physiological Concentrations of IONS:
Inside axon Outside axon Na+ 15 mM 150 mM K+ 100 mM 5 mM Cl- 13 mM 150 mM Ca++ 0.0002 mM 2 mM proteins (A-) 400 mM –
II. If the problem involves CHANGING THE ION CONCENTRATIONS INSIDE OR OUTSIDE OF THE CELL from the normal physiological concentrations to some other value, you MUST figure out how that changes the Eq for that ion. To get the new Eq, use the simplified Nernst equations above. You will find, by plugging in different numbers for the concentrations INSIDE and OUTSIDE, that the following is true:
K+: Changes from normal will greatly affect Vm of resting cell. add more K+ outside or ———-> makes Eq K+ LESS NEGATIVE decrease K+ inside cell than -80 mV —————————————————– decrease K+ outside or ———-> makes Eq K+ MORE NEGATIVE increase inside K+ than -80 mV Na+: Changes from normal will affect Vm ONLY if channels are OPEN! add more Na+ outside or ———-> makes Eq Na+ MORE POSITIVE decrease Na+ inside than +62 mV —————————————————- decrease Na+ outside or ———-> makes Eq Na+ MORE NEGATIVE increase Na+ inside than +62 mV Cl-: Changes from normal will affect Vm ONLY if channels are open. add more Cl- outside or ———–> makes Eq Cl- MORE NEGATIVE decrease Cl- inside than -65 mV —————————————————– decrease outside Cl- or ———–> makes Eq Cl- MORE POSITIVE increase Cl- inside than -65 mV
Note: add, increase, decrease, etc. means adding or reducing compared to the normal physiological concentrations of the ion.