Pharmacology and regulation of fungal K_2P channels

Fungal K_2P channels, or TOK (Two-pore Outwardly rectifying K⁺) channels, are a family of structurally and functionally unique K⁺ channels with no known homologues in animals or plants. Activation of TOK channels leads to ion dyshomeostasis and fungal cell death, but little is known about their pharmacology. Here, using two-electrode voltage clamp of Xenopus laevis oocytes, we study the effects of human K_2P channel (hK_2P) modulators on two different fungal K_2P channels cloned from human and wheat pathogens; CaTOK (Candida albicans) and MgTOK (Zymoseptoria Tritici).

CaTOK and MgTOK currents were insensitive to the hK_2P channel activator riluzole (100 µM) and hK_2P inhibitor fluoxetine (100 µM), but exhibited augmented outwardly rectifying K⁺ currents when exposed to arachidonic acid (AA) and the non-selective cyclooxygenase inhibitor BL-1249, both known hK_2P channel activators. At 0 mV, 100 µM AA increased MgTOK currents by ∼116% and CaTOK by ∼155%, whereas 100 µM BL-1249 increased MgTOK currents by ∼290% and CaTOK by ∼100%. Both AA and BL-1249 induced significant leftward shifts in the voltage of half maximal activation (V½) of MgTOK (ΔV½ = ∼40 mV and ∼30 mV respectively) and CaTOK (ΔV½ = ∼15 mV and ∼9 mV respectively). Furthermore, AA and BL-1249 also increased the rate of current activation, but were without effect on deactivation kinetics. Both CaTOK and MgTOK were insensitive to the non-selective COX inhibitor aspirin (100 µM), suggesting that their regulation by BL-1249 does not occur through the accumulation of AA via COX inhibition.

The findings are suggestive of shared regulatory mechanisms between fungal K_2P channels and their human counterparts, and highlights the need for targeted therapeutics to counter fungal infections in animals and plants.