title: Direct inhibitory action of EGTA-Ca complex on reverse-mode Na/Ca exchange in Myxicola giant axons.
abstract: Giant axons from the marine annelid Myxicola infundibulum were internally dialyzed with solutions containing 22Na ions as tracers of Na efflux. In experiments performed in Li-substituted seawater, Na efflux that is dependent on external Ca ion concentration, [Ca2+]o, was measured using dialysis to maintain [Na+]i at 100 mM, which enhances the [Ca2+]o-dependent Na efflux component, (i.e., reverse-mode Na/Ca exchange). When dialysis fluid contained EGTA (1 mM) to buffer the internal Ca concentration, [Ca2+]i, to desired levels, Na efflux lost its normal sensitivity to external calcium. The inhibition was not simply due to the Ca-chelating action of EGTA to produce insufficient [Ca2+]i to activate Na/Ca exchange. The addition of EGTA inhibited Cao-dependent Na efflux even when a large enough excess of [Ca2+]i was present to saturate the EGTA and still produce elevated values of [Ca2+]i. Control experiments showed that these high values of [Ca2+]i resulted in normal Na/Ca exchange in the absence of EGTA. It is concluded that the presence of EGTA itself interferes with the manifestation of reverse-mode Na/Ca exchange in Myxicola giant axons.
authors.affiliation: Department of Biophysics, University of Maryland School of Medicine, Baltimore 21201.
authors.forename: R A
authors.initials: RA
authors.lastname: Sjodin
authors.forename: A A
authors.initials: AA
authors.lastname: Mahmoud
authors.forename: J G
authors.initials: JG
authors.lastname: Montes
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D003956:Dialysis; D004533:Egtazic Acid / Q000378:metabolism / Q000494:pharmacology*; D066298:In Vitro Techniques; D007474:Ion Exchange; D011077:Polychaeta / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
chemical_list: D004533:Egtazic Acid; D012964:Sodium; D002118:Calcium