Ion equilibrium potentials and membrane current balance
An ion's equilibrium potential balances its chemical and electrical driving terms.
Key knowledge
An ion's equilibrium potential balances its chemical and electrical driving terms. With multiple permeant ions, membrane voltage need not equal any one equilibrium potential. A conductance model separates ionic currents from capacitive charging.
Values and equations
Ei = (RT/ziF) ln(ci,out/ci,in); Ii = gi(Vm−Ei); Iapp = Cm dVm/dt + Σi Ii
- Ei,Vm
- ion equilibrium and membrane voltages V
- R
- gas constant J mol⁻¹ K⁻¹
- T
- temperature K
- zi
- ion signed charge number 1
- F
- Faraday constant C mol⁻¹
- ci,out,ci,in
- outside/inside ion concentrations same concentration units
- gi
- whole-cell ion conductance S
- Ii,Iapp
- outward ion current and inward applied current A
- Cm
- whole-cell capacitance F
- t
- time s
Conditions and scope
- Voltage is inside minus outside; positive ionic current is outward.
- The concentration form assumes ideal activity ratios. Linear conductance is a stated approximation; real channels can gate nonlinearly.
Sources · 1
References
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Evidence and review
Read Nernst ratio, current/capacitance and conductance equations; combined current conservation explicitly, without copying malformed Goldman parentheses or quantal-failure exponent.
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Entry details
Permanent link to this entry ↗- Record identity
- uni-bio-membrane-electrical-model
- Revision
- core.1
- Structured reference record
- University core expansion