Calcium efflux and cycling across the synaptosomal plasma membrane.
Ca2+ efflux from intact synaptosomes is investigated. Net efflux can be induced by returning synaptosomes from media with elevated Ca2+ or high pH to a normal medium. Net Ca2+ efflux is accelerated when the Na+ electrochemical potential gradient is collapsed by veratridine plus ouabain. Under steady-state conditions at 30 degrees C, Ca2+ cycles across the plasma membrane at 0.38 nmol . min-1 . mg-1 of protein. Exchange is increased by 145% by veratridine plus ouabain, both influx and efflux being increased. Increased influx is probably due to activation of voltage-dependent Ca2+ channels, since it is abolished by verapamil. The results indicate that, at least under conditions of low Na+ electrochemical gradient, some pathway other than a Na+/Ca2+ exchange must operate in the plasma membrane to expel Ca2+.
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D010042:Ouabain / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*; D014701:Veratridine / Q000494:pharmacology
D010042:Ouabain; D014701:Veratridine; D012964:Sodium; D002118:Calcium