Resistance modulation in CHO cells by R-verapamil and bile salts is associated with physical and chemical changes in the cell membrane.
OBJECTIVE
Changes in multidrug resistance by resistance modifiers such as R-verapamil cause changes in fluidity of the cell membrane. The extent to which these changes involve structural alterations in membrane lipids has been investigated in CHO cells.


METHODS
Sensitive (AUXB1) and resistant (CH(R)C5) chinese hamster ovary cells (CHO) were grown in culture. Incubations were carried out with R-verapamil (0-10 microM) or the membrane perturbing agents tauro-cheno-deoxycholate (0-1.6 mM, TCDC) and tauro-urso-deoxycholate (0-3.5mM, TUDC). Cell membrane fluidity was determined by electron-paramagnetic resonance spectroscopy and membrane lipids by HPLC and TLC.


RESULTS
The resistant CH(R)C5 subline had a higher cell membrane order (lower fluidity, S = 0.7234) in the interface region of the cell membrane than sensitive AUXB1 cells (S = 0.6984) determined using EPR. The MDR-modulator R-verapamil and TCDC, but not TUDC, lowered cell membrane order in a concentration-dependent manner and increased membrane fluidity of the resistant CH(R)C5 subline. TCDC and R-verapamil were without effect on the cell membrane fluidity of AUXB1 cells. These changes were accompanied by alterations in the fatty acid composition of the plasma membrane. Untreated sensitive AUXB1 cells had higher levels of unsaturated fatty acids than resistant CH(R)C5 cells. In CH(R)C5 cells, R-verapamil increased the content of poly-unsaturated fatty acids and TCDC, but not TUDC, increased the content of mono-unsaturated fatty acids.


CONCLUSIONS
The results demonstrate that resistance modifiers such as verapamil may influence cytostatic drug action by producing structural changes to lipid domains in the plasma membrane.
Dolderer
J H
JH
Urological Clinic, Center of Surgery, Department of Surgery, Nordwest-Hospital, Frankfurt/Main, Germany.
Zimmer
G
G
Woodcock
B G
BG
Bockhorn
H
H
Bickeböller
R
R
Schuldes
H
H
D000818:Animals; D001647:Bile Acids and Salts / Q000494:pharmacology*; D016466:CHO Cells / Q000187:drug effects; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002462:Cell Membrane / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D006224:Cricetinae; D003840:Deoxycholic Acid / Q000494:pharmacology*; D018432:Drug Resistance, Multiple; D004578:Electron Spin Resonance Spectroscopy; D005227:Fatty Acids / Q000032:analysis; D005453:Fluorescence; D008560:Membrane Fluidity / Q000187:drug effects; D014700:Verapamil / Q000031:analogs & derivatives / Q000494:pharmacology*
D001647:Bile Acids and Salts; D002121:Calcium Channel Blockers; D005227:Fatty Acids; D003840:Deoxycholic Acid; D014700:Verapamil