Calcium ions regulate K⁺ uptake into brain mitochondria: the evidence for a novel potassium channel.
The mitochondrial response to changes of cytosolic calcium concentration has a strong impact on neuronal cell metabolism and viability. We observed that Ca(2+) additions to isolated rat brain mitochondria induced in potassium ion containing media a mitochondrial membrane potential depolarization and an accompanying increase of mitochondrial respiration. These Ca(2+) effects can be blocked by iberiotoxin and charybdotoxin, well known inhibitors of large conductance potassium channel (BK(Ca) channel). Furthermore, NS1619 - a BK(Ca) channel opener - induced potassium ion-specific effects on brain mitochondria similar to those induced by Ca(2+). These findings suggest the presence of a calcium-activated, large conductance potassium channel (sensitive to charybdotoxin and NS1619), which was confirmed by reconstitution of the mitochondrial inner membrane into planar lipid bilayers. The conductance of the reconstituted channel was 265 pS under gradient (50/450 mM KCl) conditions. Its reversal potential was equal to 50 mV, which proved that the examined channel was cation-selective. We also observed immunoreactivity of anti-beta(4) subunit (of the BK(Ca) channel) antibodies with ~26 kDa proteins of rat brain mitochondria. Immunohistochemical analysis confirmed the predominant occurrence of beta(4) subunit in neuronal mitochondria. We hypothesize that the mitochondrial BK(Ca) channel represents a calcium sensor, which can contribute to neuronal signal transduction and survival.
Skalska
Jolanta
J
Nencki Institute of Experimental Biology, Warsaw, Poland. Jolanta_Skalska@URMC.Rochester.edu
Bednarczyk
Piotr
P
Piwońska
Marta
M
Kulawiak
Bogusz
B
Wilczynski
Grzegorz
G
Dołowy
Krzysztof
K
Kudin
Alexei P
AP
Kunz
Wolfram S
WS
Szewczyk
Adam
A
D000818:Animals; D000906:Antibodies / Q000276:immunology; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D007150:Immunohistochemistry; D007477:Ions / Q000737:chemistry; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D010455:Peptides / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D021122:Protein Subunits / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000187:drug effects
D000906:Antibodies; D007477:Ions; C494842:Kcnma1 protein, rat; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D010455:Peptides; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D021122:Protein Subunits; C064719:iberiotoxin; D011188:Potassium; D002118:Calcium