Abstract
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.
Highlights
In tumor cells, BKCa channels regulate cell volume and shape and contribute to tumor progression and migration [3,4,5]
Functional BKCa Channels Are Present in Human Melanoma IGR39 Cells—Two types of Ca2ϩ-activated Kϩ (KCa) channels that do not depend on membrane depolarization are known to be expressed in human melanoma IGR1 and IGR39 cells, i.e. the intermediate conductance and small conductance Kϩ channels [20, 30]
We used reverse transcription-PCR (RT-PCR) to examine whether a BKCa channel, which is activated by both membrane depolarization and cytosolic Ca2ϩ, is expressed in these cells
Summary
BKCa channels regulate cell volume and shape and contribute to tumor progression and migration [3,4,5]. To test whether BKCa channels and caveolin-1 associated with each other, we performed coIP experiments using the caveolin-rich membrane fractions of IGR39 cells (supplemental Fig. S4). BKCa Channels and Naϩ/Kϩ-ATPase Interact in DRMs Depending on Membrane Cholesterol Level—Naϩ/Kϩ-ATPase, which contains caveolin-binding motifs in the ␣ subunit, has been found in caveolae of epithelial cells and was suggested to be modulated by the level of cholesterol [17].
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call