Depolarizing mammalian cardiac cells by more than 15mV above V_rest can cause le

Question

Depolarizing mammalian cardiac cells by more than 15mV above V_rest can cause lethal asynchronous heart muscle contractions known as fibrillations which essentially stop the heart's pumping action in humans. We learned in lecture that under certain conditions the concentration of K^+ outside the cardiac cells can change. What concentration of extracellular K^+ would depolarize cardiac cells by 15mV and thereby stop the heart from pumping? (Ignore any mechanisms that might remove excess K^+ from the blood and assume that the concentrations of all ions, with the exception of [K^+] _out, remain the same as given in the table below. Also, assume that the V_rest for a mammalian cardiac cell is -74mV and the permeability ratio of K^+: Na^+: Cl^- is 1: 0.02: 0.4.) You MUST show your work for credit. Please carry out your calculations to 2 decimal places.

Explanation / Answer

Nernst potential is given by the formula,

Vm = (RT/ZF) ln (Co/Ci)

R is universal gas constant

T is temperature in Kelvin

Z is the valency of ion

F is Faraday's constant

Co is extracellular ion concentration

Ci is intracellular ion concentration

-74 -(+15) = (8.314x300/1x96485) ln (x/150)

-59 = (24942/96485) ln (x/150)

-59 = 0.26 ln (x/150)

ln (x/150) = 227

ln (x) - ln (150) = 227

ln (x) - 5.02 = 227

ln (x) = 232

x = e 232

x = 5.7

The concentration of extracellular potassium is 5.7 mM.

Related Questions

Navigate

• Browse (All)
• Browse D
• Subjects

---

---

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