At rest in muscle cells, the Em is not constant but shows seemingly random fluct

Question

At rest in muscle cells, the Em is not constant but shows seemingly random fluctuations that appear to be in units of about 0.5 mV. These are called miniature endplate potentials (MEPP) and are due to the fusion of a single vesicle containing acetylcholine with the presynaptic nerve terminal membrane. A. If the muscle cell is 50 m in diameter and 10cm long, and its specific capacitance is 1 F/cm2, how much charge must flow for this 0.5mV change due to a single vesicle fusion event? B. If ENa = +66mV and Em = -85mV, and the MEPP rises in 0.5 ms, what is the average conductance increase in the membrane due to the single fusion event? Assume the current is all carried by Na+. C. How many channels do you think open during the MEPP? Use 40 pS for the unitary conductance of the acetylcholine receptor.

Explanation / Answer

Ans A. The total capacitance of the muscle fiber is CmA = 1 F/cm2 x 2 x 25 x 10-4cm x 10 cm =0.157 f.The charge can be calculated from C =Q / V so that Q = C x V = f x 0.5 mV =0.157 x 10-6 coulomb volt-1x 5 x 10-4 volt =0.785 x 10-10 coulomb = 7.85 x 10-11 coulomb

Ans. B The current is given as INA=gNA( Em- ENA), from which we can calculate the conductance. The current is 7.85 x 10-11coulomb / 5 x 10-4s = 1.57 x 10-7 amps.The driving force isEmNA= -0.085 V - 0.066 V =- 0.151 V, so that the conductance is 1.57 x 10-6amps / 0.151 V=10.40 x 10-6amps volt-1 =1.04 x 10-5siemens

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.