Activity of BK(Ca) channel is modulated by membrane cholesterol content and association with Na+/K+-ATPase in human melanoma IGR39 cells.
Interaction of large conductance Ca(2+)- and voltage-activated K(+) (BK(Ca)) channels with Na(+)/K(+)-ATPase, caveolin-1, and cholesterol was studied in human melanoma IGR39 cells. Functional BK(Ca) channels were enriched in caveolin-rich and detergent-resistant membranes, i.e. rafts, and blocking of the channels by a specific BK(Ca) blocker paxilline reduced proliferation of the cells. Disruption of rafts by selective depletion of cholesterol released BK(Ca) channels from these domains with a consequent increase in their activity. Consistently, cholesterol enrichment of the cells increased the proportion of BK(Ca) channels in rafts and decreased their activity. Immunocytochemical analysis showed that BK(Ca) channels co-localize with Na(+)/K(+)-ATPase in a cholesterol-dependent manner, thus suggesting their co-presence in rafts. Supporting this, ouabain, a specific blocker of Na(+)/K(+)-ATPase, inhibited BK(Ca) whole-cell current markedly in control cells but not in cholesterol-depleted ones. This inhibition required the presence of external Na(+). Collectively, these data indicate that the presence of Na(+)/K(+)-ATPase in rafts is essential for efficient functioning of BK(Ca) channels, presumably because the pump maintains a low intracellular Na(+) proximal to the BK(Ca) channel. In conclusion, cholesterol could play an important role in cellular ion homeostasis and thus modulate many cellular functions and cell proliferation.
Department of Medical Biochemistry and Developmental Biology, Institute of Biomedicine, University of Helsinki, Helsinki FI-00014, Finland.
Nobuyoshi
N
Tajima
Yutaka
Y
Itokazu
Esa R
ER
Korpi
Pentti
P
Somerharju
Reijo
R
Käkelä
D022461:Caveolins / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002784:Cholesterol / Q000378:metabolism*; D006801:Humans; D017136:Ion Transport; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000378:metabolism*; D008545:Melanoma / Q000378:metabolism*; D021962:Membrane Microdomains / Q000378:metabolism*; D008564:Membrane Potentials; D009363:Neoplasm Proteins / Q000378:metabolism*; D051419:Paxillin / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D022461:Caveolins; D051036:Large-Conductance Calcium-Activated Potassium Channels; D009363:Neoplasm Proteins; D051419:Paxillin; D002784:Cholesterol; D000254:Sodium-Potassium-Exchanging ATPase