A voltage-dependent K+ channel in the lysosome is required for refilling lysosomal Ca2+ stores

The resting membrane potential () of the cell is negative on the cytosolic side and determined primarily by the plasma membrane's selective permeability to K⁺. We show that lysosomal is set by lysosomal membrane permeabilities to Na⁺ and H⁺, but not K⁺, and is positive on the cytosolic side. An increase in juxta-lysosomal Ca²⁺ rapidly reversed lysosomal by activating a large voltage-dependent and K⁺-selective conductance (LysoK_VCa). LysoK_VCa is encoded molecularly by SLO1 proteins known for forming plasma membrane BK channels. Opening of single LysoK_VCa channels is sufficient to cause the rapid, striking changes in lysosomal . Lysosomal Ca²⁺ stores may be refilled from endoplasmic reticulum (ER) Ca²⁺ via ER–lysosome membrane contact sites. We propose that LysoK_VCa serves as the perilysosomal Ca²⁺ effector to prime lysosomes for the refilling process. Consistently, genetic ablation or pharmacological inhibition of LysoK_VCa, or abolition of its Ca²⁺ sensitivity, blocks refilling and maintenance of lysosomal Ca²⁺ stores, resulting in lysosomal cholesterol accumulation and a lysosome storage phenotype.

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