Inhibition of Ca(2+)-dependent K+ transport and cell dehydration in sickle erythrocytes by clotrimazole and other imidazole derivatives.

Abstract

We have investigated the interaction of clotrimazole (CLT) and related compounds with the erythroid Ca2"-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 Ca2"-activated K+ transport in homozygous hemoglobin S cells, with IC5o 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 Ca2"-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 ,gM CaCI2 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 Ca2+-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. (J. Clin. Invest. 1993. 92:520-526.)

Cation channels trigger apoptotic death of erythrocytes

“…[17][18][19] The mechanisms described here could well participate in the limitation of erythrocyte survival. The phosphatidylserine exposure at the cell surface is thought to stimulate the uptake by macrophages.…”

The antifungal antibiotic clotrimazole alters calcium homeostasis of leukemic lymphoblasts and induces apoptosis

“…7,[10][11][12][13][14][15] To determine whether clotrimazole affected Ca 2+ homeostasis in ALL cells, we measured changes in cytosolic Ca 2+ concentration in the leukemic cell line 380. Exposure to 10 m clotrimazole induced a detectable increase in cytosolic Ca 2+ concentration, as shown by an increased Indo-1 fluorescence signal ratio; this increase became clearly evident after exposure to 50 m of the drug (Figure 7).…”

“…[3][4][5][6][7][8][9] Clotrimazole disrupts cellular Ca 2+ homeostasis by releasing Ca 2+ from intracellular stores while inhibiting Ca 2+ influx and blocking IK channels. 7,[10][11][12][13][14][15] It is being evaluated clinically for the treatment of IK channel-driven erythrocyte dehydration in sickle cell dis- ease 16,17 and the treatment of secretory diarrheas that involve chloride secretion through IK channels. 18 Interest in clotrimazole as a potential antileukemic compound derives from the following observations.…”

Hemin-induced suicidal erythrocyte death

“…Cytosolic Ca 2+ concentration is increased by activation of Ca 2+ -permeable cation channels [20,21,32,41]. The increase in cytosolic Ca 2+ activity leads to activation of Ca 2+ -sensitive K + channels [9,14], which in turn results in exit of KCl with osmotically obliged water and thus in cell shrinkage [45]. The Ca 2+ sensitivity of phospholipid scrambling is increased by ceramide [42].…”