Ionophore-mediated loading of Ca2+ into large unilamellar vesicles in response to transmembrane pH gradients.
The Ca2+ translocating properties of the carboxylic ionophores A23187, ionomycin and lasolocid A (X537A) have been investigated by employing large unilamellar vesicles that exhibit a pH gradient (acidic interior). An analysis of Ca2+ uptake at equilibrium reveals that Ca2+ accumulation is an electroneutral process, whereby one Ca2+ ion is transported in for every two H+ ions transported out. A kinetic analysis shows that both A23187 and ionomycin transport Ca2+ in the form of a 1:1 cation:ionophore complex, whereas a 1:2 complex is observed for lasolocid A. The specificity of the ionophores for transporting Ca2+ is reflected by the influence of exterior Na+ ions that inhibit Ca2+ uptake for lasolocid A but do not influence ionomycin-mediated uptake.
Wheeler
J J
JJ
Department of Biochemistry, University of British Columbia, Vancouver, Canada.
Veiro
J A
JA
Cullis
P R
PR
D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000493:pharmacokinetics*; D002412:Cations / Q000493:pharmacokinetics; D006863:Hydrogen-Ion Concentration; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology*; D007700:Kinetics; D008081:Liposomes / Q000737:chemistry; D008566:Membranes / Q000737:chemistry / Q000187:drug effects
D002412:Cations; D007476:Ionophores; D008081:Liposomes; D000001:Calcimycin; D015759:Ionomycin; D002118:Calcium