This thesis describes two groups of experiments, both relating to the
condition of distal renal tubular acidosis (dRTA).
In the first, an alternative diagnostic test of dRTA to the ‘gold standard’
short ammonium chloride (NH4Cl) test was assessed. This was achieved
by the simultaneous oral administration of the diuretic furosemide and
the mineralocorticoid fludrocortisone to increase distal sodium delivery
and a-intercalated cell proton secretion. I evaluated 11 control subjects
and 10 patients with known dRTA by giving oral NH4Cl or
furosemide/fludrocortisone in random order on separate days. 3
subjects were unable to complete the study due to vomiting after the
NH4Cl, however there were no adverse effects with
furosemide/fludrocortisone administration. The urine pH decreased to
less than 5.3 in the controls with both tests, whereas no patients were
able to lower their urine pH below 5.3 with either test. The simultaneous
administration of furosemide/fludrocortisone proved to be an easy,
effective and well-tolerated alternative to the standard NH4Cl test for the
diagnosis of dRTA.
The second group were laboratory-based molecular physiology
experiments. Anion exchanger 1 (AE1) mediates electroneutral anion
exchange across cell membranes. It is the most abundant protein in the
red cell membrane, but is also found in the basolateral membrane of
renal a-intercalated cells, where it is required for urinary acidification.
Point mutations have been described that convert the red cell AE1 into a
cation conductance. AE1 mutations can also cause hereditary dRTA. I
investigated the properties of four dRTA associated AE1 mutations
(R586H, G609R, S613F and G701D) by heterologous expression in
Xenopus Laevis oocytes. These mutants proved to be functional anion
exchangers, unlike the red cell mutants, but also demonstrated a cation
‘leak’. I found a very large leak property in the G701D mutant, which is
prevalent in SE Asia. I hypothesised that this property might confer a survival advantage. I characterised three other AR dRTA-associated AE1
mutants found in SE Asia, S773P, \Delta850 and A858D via similar transport
experiments in AE1-expressing Xenopus oocytes. These three SE Asian
mutants also had cation leaks of similar magnitude to that seen in
G701D, a property that distinguishes them as a discrete group. The
clustering of these cation-leaky AE1 mutations to malarious areas of SE
Asia suggests that they may confer malaria resistance
