Abstract

Objectives: 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 (CHRC5) chinese hamster ovary cells (CHO) were grown in culture. Incubations were carried out with R-verapamil (0 – 10 mM) 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 CHRC5 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 CHRC5 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 CHRC5 cells. In CHRC5 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.

Author Details

Authors

• J.H. Dolderer¹,⁴
• G. Zimmer²
• B.G. Woodcock³
• H. Bockhorn⁴
• R. Bickeböller¹
• H. Schuldes⁴

Departments

• ¹ Cellular Research Laboratory of the Urological Clinic, Center of Surgery,
• ² Membrane Structure Group, Center of Biological Chemistry,
• ³ Institute of Clinical Pharmacology,
• ⁴ Department of Surgery, Nordwest-Hospital, Johann-Wolfgang-Goethe-University Hospital, Frankfurt/Main and
• ⁵ Urology Department, St. Katharinen-Hospital, Frechen, Germany

Address

Dr. B.G. Woodcock; Institut für Klinische Pharmakologie, Universitätsklinik Frankfurt, Theodor-Stern-Kai 7, D-60590 Frankfurt, Germany
Email: woodcock@em. uni-frankfurt.de

Citation