Transport Properties of the Calcium Ionophore ETH-129

• Published in: Biophysical journal 2001-12, Vol.81 (6), p.3275-3284
• Main Authors: Wang, Exing, Erdahl, Warren L., Hamidinia, Shawn A., Chapman, Clifford J., Taylor, Richard W., Pfeiffer, Douglas R.
• Format: Article
• Language: English
• Subjects: Biochemistry; Biological Transport; Calcimycin - pharmacology; Calcium; Calcium - metabolism; Cations; Cellular biology; Cyclohexanes - chemistry; Cyclohexanes - pharmacology; Dose-Response Relationship, Drug; Enzyme Inhibitors; Hydrazones - chemistry; Hydrogen-Ion Concentration; Ionomycin - pharmacology; Ionophores - chemistry; Ionophores - pharmacology; Ions; Kinetics; Membrane Potentials; Models, Chemical; Molecules; Phospholipids - chemistry; Potassium - chemistry; Protein Transport; Time Factors
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(01)75961-9

The transport mechanism and specificities of ionophore ETH-29 have been investigated in a highly defined phospholipid vesicle system, with the goal of facilitating the application of this compound to biological problems. ETH-129 transports Ca 2+ via an electrogenic mechanism, in contrast to A23187 and ionomycin, which function in a charge neutral manner. The rate of transport is a function of membrane potential, increasing by 3.9-fold per 59 mV over a broad range of that parameter. Rate is independent of the transmembrane pH gradient and strongly stimulated by the uncoupler carbonyl cyanide m-chlorophenylhydrazone when no external potential has been applied. The effect of uncoupler reflects the collapse of an opposing potential arising during Ca 2+ transport, but also reflects the formation of a mixed complex between the uncoupler, ETH-129, and Ca 2+ that readily permeates the vesicle membrane. Oleate does not substitute for the uncoupler in either regard. ETH-129 transports polyvalent cations according to the selectivity sequence La 3+ > Ca 2+ > Zn 2+ ≈ Sr 2+ > Co 2+ ≈ Ni 2+ ≈ Mn 2+, with the magnitude of the selectivity coefficients reflecting the cation concentration range considered. There is little or no activity for the transport of Na +, K +, and Mg 2+. These properties suggest that ETH-129 will be useful for investigating the consequences of a mitochondrial Ca 2+ overload in mammalian cells, which is difficult to pursue through the application of electroneutral ionophores.