Ion conductance pathways in potato tuber (Solanum tuberosum) inner mitochondrial membrane

Single-ion channel activities were measured after reconstitution of potato tuber mitochondrial inner membranes into planar lipid bilayers. In addition to the recently described large-conductance Ca2+-activated potassium channel activity (Koszela-Piotrowska et al., 2009), the following mitochondrial ion conductance pathways were recorded: (i) an ATP-regulated potassium channel (mitoKATP channel) activity with a conductance of 164 ± 8 pS, (ii) a large-conductance Ca2+-insensitive iberiotoxin-sensitive potassium channel activity with a conductance of 312 pS ± 23, and (iii) a chloride 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS)-inhibited channel activity with a conductance of 117 pS ± 4. In isolated non-phosphorylating potato tuber mitochondria, individual and combined potassium channel activities caused significant (up to 14 mV) but not collapsing K+-influx-induced membrane potential depolarisation. Under phosphorylating conditions, the coupling parameters were unchanged in the presence of high K+ level, indicating that plant K+ channels function as energy-dissipating systems that are not able to divert energy from oxidative phosphorylation. A potato tuber K+ channel that is ATP-, 5-hydroxydecanonic acid-, glybenclamide-inhibited and diazoxide-stimulated caused low cation flux, modestly decreasing membrane potential (up to a few mV) and increasing respiration in non-phosphorylating mitochondria. Immunological analysis with antibodies raised against the mammalian plasma membrane ATP-regulated K+ channel identified a pore-forming subunit of the Kir-like family in potato tuber mitochondrial inner membrane. These results suggest that a mitoKATP channel similar to that of mammalian mitochondria is present in potato tuber mitochondria.

Research Highlights
► MitoBK channels, mitoKATP channel and mitoCl channel are detected in potato tuber mitochondria.
► Plant K channels function as energy-dissipating systems that do not decrease ATP synthesis yield.
► MitoKATP channel in potato tuber mitochondria is similar to that of mammalian mitochondria.