Changes in membrane cholesterol of pituitary tumor (GH3) cells regulate the activity of large-conductance Ca2+-activated K+ channels.
The effects of changes in membrane cholesterol on ion currents were investigated in pituitary GH3 cells. Depletion of membrane cholesterol by exposing cells to methyl-beta-cyclodextrin (MbetaCD), an oligosaccharide, resulted in an increase in the density of Ca2+-activated K+ current (IK(Ca)). However, no significant change in IK(Ca) density was demonstrated in GH3 cells treated with a mixture of MbetaCD and cholesterol. Cholesterol depletion with MbetaCD (1.5 mg/ml) slightly suppressed the density of voltage-dependent L-type Ca2+ current. In inside-out patches recorded from MbetaCD-treated cells, the activity of large-conductance Ca2+-activated K+ (BK(Ca)) channels was enhanced with no change in single-channel conductance. In MbetaCD-treated cells, voltage-sensitivity of BK(Ca) channels was increased; however, no change in Ca2+-sensitivity could be demonstrated. A negative correlation between adjacent closed and open times in BK(Ca) channels was observed in MbetaCD-treated cells. In inside-out patches from MbetaCD-treated cells, dexamethasone (30 microM) applied to the intracellular surface did not increase BK(Ca)-channel activity, although caffeic acid phenethyl ester and cilostazol still opened its probability effectively. However, no modification in the activity of ATP-sensitive K+ channels could be seen in MbetaCD-treated cells. Current-clamp recordings demonstrated that the cholesterol depletion maneuver with MbetaCD reduced the firing of action potentials. Therefore, the increase in BK(Ca)-channel activity induced by membrane depletion may influence the functional activities of neurons or neuroendocrine cells if similar results occur in vivo.
Lin
Ming-Wei
MW
Institute of Basic Medical Sciences, Medical College, National Cheng Kung University, Tainan 70101, Taiwan, ROC.
Wu
Adonis Z
AZ
Ting
Wen-Hung
WH
Li
Ching-Lin
CL
Cheng
Kuo-Sheng
KS
Wu
Sheng-Nan
SN
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002109:Caffeic Acids / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002784:Cholesterol / Q000502:physiology*; D000077407:Cilostazol; D003907:Dexamethasone / Q000494:pharmacology; D003981:Diazoxide / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000187:drug effects* / Q000502:physiology; D008563:Membrane Lipids / Q000502:physiology*; D010626:Phenylethyl Alcohol / Q000031:analogs & derivatives / Q000494:pharmacology; D010911:Pituitary Neoplasms / Q000503:physiopathology*; D051381:Rats; D013777:Tetrazoles / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D047392:beta-Cyclodextrins / Q000494:pharmacology
D002109:Caffeic Acids; D007211:Indoles; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008563:Membrane Lipids; D013777:Tetrazoles; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D001030:Apamin; C048220:paxilline; D003907:Dexamethasone; D002784:Cholesterol; C055494:caffeic acid phenethyl ester; D010626:Phenylethyl Alcohol; D000077407:Cilostazol; D003981:Diazoxide; D005905:Glyburide; D002118:Calcium