Question

Table 1 - a partial list of Elaina's Vital Signs vitals Elaina Normal blood pessure 126/84 (hypertension) 90-120/60/80 pulse rate 105 bpm (tachycardia) 60-100 bpm temperature 98.8 F 98.6 F Table 2- A Partial list of results from Elaina's blood work measurement Elaina Normal White blood cell count 7,800 cells/mm^3 4500-10,500 cells/mm^3 sodium (mM) 142 135-145 potassium (mM) 6.2 3.5-5.2 Triiodothyronine (T3) (ng/dL) 11.2 59-174 Tetraiodothyronine or thyroxine (T4) (ng/dL) 7.3 4.5-12 Thyroid Stimulation Hormone (TSH) (ng/dL) 1.8 0.3-3.0 1. Use the Nernst equation (below) to calculate the equilibrium potential for potassium in a normal patient and in Elaina. Assume that the ion level in the interstitial fl uid is the same as that in the blood plasma, and also assume that the intracellular concentration of potassium is 150 mM in Elaina and in normal patients. E K+ (millivolts) = 61 log10 ([K+]out /[K+]in) Table 1 - a partial list of Elaina's Vital Signs vitals Elaina Normal blood pessure 126/84 (hypertension) 90-120/60/80 pulse rate 105 bpm (tachycardia) 60-100 bpm temperature 98.8 F 98.6 F Table 2- A Partial list of results from Elaina's blood work measurement Elaina Normal White blood cell count 7,800 cells/mm^3 4500-10,500 cells/mm^3 sodium (mM) 142 135-145 potassium (mM) 6.2 3.5-5.2 Triiodothyronine (T3) (ng/dL) 11.2 59-174 Tetraiodothyronine or thyroxine (T4) (ng/dL) 7.3 4.5-12 Thyroid Stimulation Hormone (TSH) (ng/dL) 1.8 0.3-3.0 1. Use the Nernst equation (below) to calculate the equilibrium potential for potassium in a normal patient and in Elaina. Assume that the ion level in the interstitial fl uid is the same as that in the blood plasma, and also assume that the intracellular concentration of potassium is 150 mM in Elaina and in normal patients. E K+ (millivolts) = 61 log10 ([K+]out /[K+]in)

Answer 1

The equilibrium potentials are calculated using the given form of Nernst equation ,ie.

E_K+  = 61 log [ K⁺ ] _out / [ K⁺ ]_in

[ K⁺ ]_in   = 150 mM ........(given for all conditions )

& [ K⁺ ]_out varies from 3.5 - 5.2 , 6.2 mM .........( given )

Hence, substitution of the given values in Nenst equation we get the results as worked out below ,

E_K⁺ = 61 log [ K⁺ ]_out / [ K⁺ ]_in

..............................................I.........................II...............................................III

E_K⁺ in milivolts = 61 log 6.2 / 150............61 log 3.5 /150.....................61 log 5.5 /150

.......................... = 61log 0.041333............61 log 0.023333..................61log 0.036666  

.......................... = - 84.40 mV..................- 99.55mV.............................- 87.5.................