The energy cost of kidney proton dialysis in sickle cell anaemia

The acidosis known to be associated with sickle cell anaemia is exploited in this work to estimate its energy cost to the kidney that has to dialyse the excess protons from the blood into urine against a concentration gradient, thereby doing significant extra work. The mean blood and urine pHs measured for the four discrete sickle cell states (42 subjects with approximately equal numbers of males and females per group, to minimise sex bias) are: HbAA = 7.39 +/- 0.07 and 6.54 +/- 0.15, HbAS = 7.35 +/- 0.09 and 6.44 +/- 0. 15, HbSS = 7.32 +/- 0.08 and 5.89 +/- 0. 39, HbSS-crisis = 7.15 +/- 0.12 and 4.75 +/- 0.46, respectively. From these data, the estimated enthalpies of dialysis, Delta H-d, for each of the four states are: HbAA = 1.96RT approximate to 4.94 kJ, HbAS = 2.10RT approximate to 5.29 kJ, HbSS = 3.29RT approximate to 8.29 kJ, and HbSS-crisis = 5.53RT approximate to 13.93 kJ. The estimated entropies of dialysis, T Delta S-d, compared to the normal HbAA state are: HbAA = 0.00RT approximate to 0.00 kJ; HbAS = 0.14RT approximate to 0.35 kJ, HbSS = 1.34RT approximate to 3.38 kJ and HbSS-crisis = 3.57RT approximate to 8.99 kJ (R = 8.31J-mol(-1) K-1 and T = 303K). The conclusion from this work is that sickle cell disease is very energy costly to the kidney as most of the energy for proton dialysis is wasted as a result of high entropy.