Calcium influx factor directly activates store-operated cation channels in vascular smooth muscle cells.
Recently, we described a novel 3-pS Ca(2+)-conducting channel that is activated by BAPTA and thapsigargin-induced passive depletion of intracellular Ca(2+) stores and likely to be a native store-operated channel in vascular smooth muscle cells (SMC). Neither Ca(2+) nor inositol 1,4,5-trisphosphate or other second messengers tested activated this channel in membrane patches excised from resting SMC. Here we report that these 3-pS channels are activated in inside-out membrane patches from SMC immediately upon application of Ca(2+) influx factor (CIF) extracted from mutant yeast, which has been previously shown to activate Ca(2+) influx in Xenopus oocytes and Ca(2+) release-activated Ca(2+) current in Jurkat cells. In bioassay experiments depletion of Ca(2+) stores in permeabilized human platelets resulted in the release of endogenous factor, which activated 3-pS channels in isolated inside-out membrane patches excised from SMC and exposed to permeabilized platelets. The same 3-pS channels in excised membrane patches were also activated by acid extracts of CIF derived from human platelets with depleted Ca(2+) stores, which also stimulated Ca(2+) influx upon injection into Xenopus oocytes. Specific high pressure liquid chromatography fractions of platelet extracts were found to have CIF activity when injected into oocytes and activate 3-pS channels in excised membrane patches. These data show for the first time that CIF produced by mammalian cells and yeast with depleted Ca(2+) stores directly activates native 3-pS cation channels, which in intact SMC are activated by Ca(2+) store depletion.
Trepakova
E S
ES
Vascular Biology Unit, Department of Medicine, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
Csutora
P
P
Hunton
D L
DL
Marchase
R B
RB
Cohen
R A
RA
Bolotina
V M
VM
D000818:Animals; D001685:Biological Factors / Q000378:metabolism*; D001792:Blood Platelets / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D008564:Membrane Potentials; D051379:Mice; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology; D014981:Xenopus
D001685:Biological Factors; D015220:Calcium Channels; D004533:Egtazic Acid; D019284:Thapsigargin; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid