Detachment of Cytochrome c by Cationic Drugs from Membranes Containing Acidic Phospholipids: Comparison of Lidocaine, Propranolol, and Gentamycin
- Department of Medical Chemistry, Institute of Biomedicine, FIN-00014 University of Helsinki, Finland
Abstract
A large number of pharmaceutically active compounds have a high affinity to acidic phospholipids; good examples are the cationic compounds lidocaine, propranolol, and gentamycin. These drugs influenced the lipid dynamics of liposomes composed of phosphatidylcholine and the acidic phosphatidylglycerol, as judged by the excimer/monomer emission intensity ratio for a pyrene-labeled phospholipid analog, as well as by polarization of DPH fluorescence. When the mole fraction X of PG (XPG) was 0.20, lidocaine increased membrane fluidity. The opposite was true for propranolol, which caused the formation of pyrene lipid-enriched microdomains. Gentamycin had no apparent effect. At XPG = 1.00, all these drugs rigidified membrane. Subsequently, we investigated the detachment of a cationic peripheral membrane protein, cytochrome c(cyt c), by these compounds from liposomes. This was accomplished by monitoring resonance energy transfer from a pyrene-labeled phospholipid to the heme of cyt c. The efficiency of the above compounds to dissociate cyt cvaried considerably. In brief, significantly lower concentrations of gentamycin than propranolol or lidocaine were required for half-maximal dissociation of cyt c from liposomes, although the final extent of protein detachment by gentamycin was less complete. ATP augmented the dissociation of cyt c from membranes by lidocaine and propranolol. Stopped-flow measurements also revealed that the half-times differed for the release of cyt c from the membranes. Our results are likely to reflect differences in the contributions of the electrostatic interactions and hydrophobicity to the drug/lipid interaction and comply with two different acidic phospholipid binding sites in cyt c.
Footnotes
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Send reprint requests to: Dr. Paavo K. J. Kinnunen, Department of Medical Chemistry, Institute of Biomedicine, University of Helsinki, P.O. Box 8 (Siltavuorenpenger 10A), FIN-00014 Helsinki, Finland. E-mail:paavo.kinnunen{at}helsinki.fi
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This work was supported by Finnish State Medical Research Council and Biocenter Helsinki.
- Abbreviations:
- cyt c
- cytochromec
- DPH
- 1,6-diphenyl-1,3,5-hexatriene
- PC
- phosphatidylcholine
- PG
- phosphatidylglycerol
- Ie/Im
- ratio of excimer and monomer fluorescence
- LUV
- large unilamellar vesicle
- POPC
- 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine
- POPG
- 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol
- HEPES
- 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- PPDPG
- 1-palmitoyl-2[10-(pyren-1-yl)]decanoyl-sn-glycero-3-phosphatidylglycerol
- RET
- resonance energy transfer
- RFI
- relative fluorescence intensity
- Xlipid
- mole fraction of the indicated lipid
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- Received December 26, 1997.
- Accepted June 18, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
