Similarity in calcium channel activity of annexin V and matrix vesicles in planar lipid bilayers.
Matrix vesicles (MVs), structures that accumulate Ca2+ during the initiation of mineral formation in growing bone, are rich in annexin V. When MVs are fused with planar phospholipid bilayers, a multiconductance Ca2+ channel is formed, with activity essentially identical to that observed when annexin V is delivered to the bilayer with phosphatidylserine liposomes. Ca2+ currents through this channel, from either MV or annexin V liposomes, are blocked by Zn2+, as is Ca2+ uptake by MV incubated in synthetic cartilage lymph. Blockage by Zn2+ was most effective when applied to the side containing the MV or liposomes. ATP and GTP differentially modulated the activity of this channel: ATP increased the amplitude of the current and the number of conductance states; GTP dramatically reduced the number of events and conductance states, leading to well-defined Ca2+ channel activity from either MV or the annexin V liposomes. In the distinctive effects of ATP, GTP, and Zn2+ on the Ca2+ channel activity observed in both the MV and the liposome systems, the common factor was the presence of annexin V. From this we conclude that Ca2+ entry into MV results from the presence of annexin V in these membrane-enclosed structures.
Laboratory of Cell Biology and Genetics, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
N
N
Arispe
E
E
Rojas
B R
BR
Genge
L N
LN
Wu
R E
RE
Wuthier
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D017304:Annexin A5 / Q000302:isolation & purification / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D002645:Chickens; D017364:Collagenases; D004553:Electric Conductivity; D005109:Extracellular Matrix / Q000502:physiology* / Q000648:ultrastructure; D006160:Guanosine Triphosphate / Q000494:pharmacology; D008051:Lipid Bilayers; D008561:Membrane Fusion; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008861:Microsomes / Q000502:physiology*; D014357:Trypsin; D015032:Zinc / Q000494:pharmacology
D017304:Annexin A5; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D008051:Lipid Bilayers; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D014357:Trypsin; D017364:Collagenases; D015032:Zinc; D002118:Calcium