4/6/2023 0 Comments Int1 task3![]() In contrast to its animal counterpart, MpBK2a is insensitive to cytoplasmic Ca2+ variations but effectively gated by pH changes. We characterised MpBK2a channels and found them to be strongly K+-selective, outward-rectifying, 80-pS channels capable of repolarising the membrane after stimulus-dependent depolarisation. In the liverwort Marchantia polymorpha, the MpBK2a channel gene is most highly expressed in male reproductive tissue, suggesting that these channels may function in sexual reproduction. In humans, BK-mediated K+ efflux has a critical role in sperm motility and membrane polarisation to enable fertilisation. ![]() While the function and gating of Shaker channels has been characterised in flowering plants, so far knowledge of BK channels has been limited to animal models. Based on their presence in extant embryophytes and closely-related green algae, the first plants to survive on land likely possessed genes encoding channels with homology to large-conductance calcium-activated K+ channels (BK channels from the Slo family) in addition to primary voltage-gated potassium channels from the plant VG-type family (Shaker or Kv channels). Voltage-dependent ion channels are a prerequisite for cellular excitability and electrical communication - important traits for multicellular organisms to thrive in a changeable terrestrial environment. (G) Macroscopic currents of mSlo1D133A147A at 519 (F) The G-V 517 curves of D147A at pH O 7 or 4. (E) Macroscopic currents of mSlo1D147A at pH O 7 (left) or pH 4 (right). ![]() (D) The G-V curves of D133A at pH O 7 or 4. Dotted lines 513 in this and following G-V plots are the G-V curves of WT channels at pH7 (black) or 4 (red) with 300 M in (C) 514 Macroscopic currents of mSlo1D133A at pH O 7 (left) or pH 4 (right). The number of patches contributing to each set of G-V 511 relationship is given in parentheses in this and following G-V plots. (B) The G-V curves of D153A at pH O 7 or 4. All pipette (intracellular) solutions contained 300 510 M Ca 2+. All other currents shown in this figure were 509 evoked by steps from-120 to +200 mV (20 mV increments). The currents of D153A were 508 evoked by steps from-160 to +240 mV with 20 mV increments. (A) Macroscopic currents of 507 mSlo1D153A from an outside-out patch perfused at pH O 7 (left) or pH O 4 (right). Given that these key residues (D133, D147, D153) are highly conserved among members in the voltage-dependent cation channel superfamily, the mechanism underlying BK inhibition by extracellular acidification might also be applicable to other members in the family.Īcidic residues involved in BK inhibition induced by extracellular H +. Our results reveal that this inhibition is mainly caused by H+ inhibition of BK voltage-sensor (VSD) activation through three acidic residues on the extracellular side of BK VSD. Here we show that BK activation is strongly and reversibly inhibited by extracellular H+, with its conductance-voltage relationship shifted by more than +100 mV at pHO 4. For example, it has been reported that BK channels are expressed in lysosomes with their extracellular side facing the strongly acidified lysosomal lumen (pH ~ 4.5). Among different loci, the composition of the extracellular microenvironment, including pH, may differ substantially. ![]() Mammalian BK-type voltage- and Ca2+-dependent K+ channels are found in a wide range of cells and intracellular organelles.
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