Specific Inhibition of the Plasmodial Surface Anion Channel by Dantrolene

Abstract

The plasmodial surface anion channel (PSAC), induced on human erythrocytes by the malaria parasite Plasmodium falciparum, is an important target for antimalarial drug development because it may contribute to parasite nutrient acquisition. However, known antagonists of this channel are quite nonspecific, inhibiting many other channels and carriers. This lack of specificity not only complicates drug development but also raises doubts about the exact role of PSAC in the well-known parasite-induced permeability changes. We recently identified a family of new PSAC antagonists structurally related to dantrolene, an antagonist of muscle Ca ؉؉ release channels. Here, we explored the mechanism of dantrolene's actions on parasite-induced permeability changes. We found that dantrolene inhibits the increased permeabilities of sorbitol, two amino acids, an organic cation, and hypoxanthine, suggesting a common pathway shared by these diverse solutes. It also produced parallel reductions in PSAC single-channel and whole-cell Cl ؊ currents. In contrast to its effect on parasite-induced permeabilities, dantrolene had no measurable effect on five other classes of anion channels, allaying concerns of poor specificity inherent to other known antagonists. Our studies indicate that dantrolene binds PSAC at an extracellular site distinct from the pore, where it inhibits the conformational changes required for channel gating. Its affinity for this site depends on ionic strength, implicating electrostatic interactions in dantrolene binding. In addition to the potential therapeutic applications of its derivatives, dantrolene's specificity and its defined mechanism of action on PSAC make it a useful tool for transport studies of infected erythrocytes.

Changes in the Plasmodial Surface Anion Channel Reduce Leupeptin Uptake and Can Confer Drug Resistance in Plasmodium falciparum -Infected Erythrocytes

“…4C). Concordant changes in the osmotic lysis assay and in single channel recordings are consistent with a primary role for PSAC in the uptake of diverse organic solutes, as suggested in various other studies (2,5,9,10,14,15,17).…”

“…In vitro selection of specifically engineered changes in human ion channels permitting reduced leupeptin entry but the sustained uptake of nutrients is difficult to envision, especially because erythrocytes lack heritable genetic material. Second, NPF-1 has no measurable ac- on May 12, 2018 by guest http://aac.asm.org/ tivity against a battery of other ion channels in other systems (15,17). To account for the reduced leupeptin uptake in HB3-leuR1, a channel unrelated to PSAC would need to be present on the erythrocyte membrane and also be sensitive to NPF-1, an unlikely coincidence.…”

Maduramicin Rapidly Eliminates Malaria Parasites and Potentiates the Gametocytocidal Activity of the Pyrazoleamide PA21A050

“…These findings are in marked contrast to those obtained with other gametocytocidal agents, such as the diaminonaphthoquinones (DANQs) and the proteasome inhibitor epoxomicin, which require 72 h to decrease late-stage gametocyte viability to Ͻ10% (26). The similar time courses of the decrease in membrane potential following maduramicin treatment of late-stage gametocytes and asexual Plasmodium parasites suggests that asexual parasite-specific cellular activities, such as hemoglobin digestion, DNA replication, or the presence of a plasmodial surface anion channel (PSAC) on the RBC surface, do not influence the efficacy of maduramicin (33)(34)(35)(36). These processes have previously been identified as targets for compounds that preferentially affect asexual parasites, including pyrimethamine, chloroquine, and furosemide.…”

Selective killing of the human malaria parasite Plasmodium falciparum by a benzylthiazolium dye

“…The molecular identity of the channel remains a mystery and there is some controversy as to whether and if the channel is composed of proteins derived from the parasite or simply remodeled from host proteins (Kirk, 2000). But despite this uncertainty there is a clear recognition that the channel is an attractive target for new drug design (Alkhalil, et al, 2004,Desai, 2004,Ginsburg and Stein, 2005,Kirk, 2004,Lisk, et al, 2006. It is hoped that the results reported here will aid in the effort to develop pharmacologic means to block or subvert the channel, leading to discovery of novel antimalarial agents.…”