We have investigated the interaction of
clotrimazole (CLT) and related compounds with the erythroid Ca(2+)-activated K+ channel, a mediator of sickle cell
dehydration. We measured K+ transport, membrane potential, and cell volume upon activation of this pathway in sickle erythrocytes. CLT blocked almost completely Ca(2+)-activated K+ transport in homozygous
hemoglobin S cells, with IC50 values of 29 +/- 15 nM in isotonic 20 mM
salt solution and 51 +/- 15 nM in
normal saline (n = 3). The inhibition of K+ transport by CLT was caused by a specific interaction with the Ca(2+)-activated K+ channel of human red cells, since it displaced bound 125I-Charybdotoxin, a specific
ligand of the Gardos channel, with an IC50 (12 +/- 4 nM in isotonic 20 mM) similar to the IC50 values for flux inhibition. When homozygous
hemoglobin S cells were dehydrated by incubation in the presence of 100 microM CaCl2 and the
ionophore A23187, or by exposure to cycles of oxygenation and deoxygenation, CLT effectively inhibited cell
dehydration and K+ loss. The IC50 of CLT for inhibition of Ca(2+)-activated K+ transport in sickle cells is significantly lower than plasma concentrations of CLT achievable after nontoxic oral doses. We therefore propose that
oral administration of CLT may prevent red cell
dehydration in patients with
sickle cell anemia.