2. The resting concentration of calcium ions, Ca (valence Z=2 for calcium), is about Cin = 10-3 mole/liter in the extracellular space but is very low (Cout =10 mole/liter) inside muscle cells. Determine the membrane potential AV for calcium. Suppose diffusion temperature T = 27 °C. BIOELECTRICITY. MEMBRANE POTENTIALS 1. Electrical charge. There are only two types of charge, which we call positive (proton) and negative (electron). Charge of electron and proton is e =1.6x10"C. Mass of electron 9.1x10" kg and mass of proton 1.67x10" kg. Then, electrical charge is q = Ne, here N amount of charged particles. 2. The electric field E is defined to be E = where F is the Coulomb or electrostatic force exerted on a small positive test charge q. E has units of N/C. The magnitude of the electric field E created by a point charge q is F = k where r is the distance from q. The electric field E is a vector and fields due to multiple charges add like vectors. 3. The potential difference between points A and B, ViB – Va , defined to be the change in potential energy of a charge q moved from A to B, is equal to the change in potential energy divided by the charge, Potential difference is commonly called voltage, represented by the symbol AV: AV = 4. In uniform electric field the potential difference is Av = Ed, where E is electric field and d is the distance from A to B, or the distance between the plates. 5. A capacitor is a device used to store charge. The amount of charge q a capacitor can store depends on two major factors - the voltage applied and the capacitor's physical characteristics, such as its size. The capacitance C is the amount of charge stored per volt, or C = units Farad (F). 6. Capacitance of a parallel plate capacitor C = 4, where ɛg = 8.85 · 10-12 F/m is called the permittivity of free space, e is the dielectric constant of the material, A is area of plates and d is distance between plates. 7. Capacitors are used in a variety of devices, including defibrillators, microelectronics such as calculators, and flash lamps, to supply energy. The energy stored in a capacitor can be expressed in three APE AV CAV2 ways: Energy = of the capacitor(F). 8. Electric current / is the rate at which charge flows, given by I =, units Amperes (A). Here q is the amount of charge passing through an area in time t. where q is the charge (C), AV is the voltage (V), and C is the capacitance = Menbrane 9. Membrane potential is potential difference between inner and outer surface of biological membrane. The semipermeable membrane of a cell concentrations of ions inside and out. Diffusion moves the Inside Coulonb force has different Ditusion Outside K* and Cl ions in the direction shown, until the Coulomb force halts further transfer. This results in a layer of positive charge on the outside, a layer of negative charge on the inside, and thus a voltage across the cell membrane. At rest state, the membrane is normally impermeable to Na". If Coulomb tato Ditusion -Coulomb force Ditusion membrane is pemeable only to one ion type, the membrane potential is determined by equation: AV = In , here R = 8,31J/(mole-K) is gas constant; Tis the temperature of diffusion (K); F = 96500 C/mole is Faraday's constant, Z is valence of ion (Z = 1 for K*, Na*, Cl"), Cin is the ions concentration inside the cell (mole/m) and Cout is the ions concentration outside the cell (mole/m). If membrane is permeable simultaneously to three ion types, then the membrane potential is found by RT Cin Cout cquation: RT, PCA + PNaC" + PeiCsut + PxaC + PeC In- AV = - PCout ZF here Px, PNa, Pa are permeability of the membrane to corresponding ion type C, C, C are ions concentrations inside the cell (mole/m) and Cout, Cot, Cout are corresponding concentrations outside the cell (mole/m'). CNa