The I nf l uence of Chem i cal Agent s on t he Level of I oni zed [Ca 2+] in Squi d Axons J . REQUENA, J . WHI TTEMBURY, T. TI FFERT, D . A . EI SNER, and L . J . MULLI NS Fr om t he Cent ro de Bi oci enci as, I nst i t ut o I nt er naci onal de Estudi os Avanzados (I DEA), Car acas, Venezuel a; t he Labor at or y of Bi ophysi cs, Uni versi dad Cayet ano Heredi a, Lima, Per u ; t he Department of Physi ol ogy, Uni versi t y Col l ege London, London, Engl and; and t he Department of Bi ophysi cs, Uni versi ty of Maryl and School of Medi ci ne, Bal ti more, Maryl and 21201 ABSTRACT Squi d gi ant axons i nj ect ed wi th ei t her aequor i n or ar senazo III and bat hed in 3 mM Ca (Na) seawat er wer e t r ansf er r ed to 3 mM Ca (K) seawat er and t he r esponse of t he aequor i n l i ght or t he change in t he absor bance of ar senazo III was fol l owed. These experi ment al condi t i ons wer e chosen because t hey measur e t he change in t he r at e of Na/ Ca exchange in i nt r oduci ng Ca i nt o t he axon upon depol ar i zat i on ; [ Cal . i s t oo l owt o ef f ect a channel - based syst em of Ca ent r y. Thi s pr ocedur e was appl i ed to axons t r eat ed w itha var i et y of compounds t hat have been i mpl i cated as i nhi bi t ors of Na/ Ca exchange. The r esul t obt ai ned was t hat t he subst ances t est ed coul d be pl aced in t hr ee gr oups . ( a) Subst ances t hat wer e w i t hout ef f ect on Ca ent r y ef f ect ed by Na/ Ca exchange wer e: D600 at 10- 100 FM , ni t r endi pi ne at 1- 5 uM , Ba 2+ and Mg" at concen- t r at i ons of 10- 50 mM , l i docai ne at 0. 1- 10 mM , cyani de at 2 mM , adri amyci n at a concent r at i on of 3, M , chl or adenosi ne at 35 , AM , 2, 4- di am i nopyr i di ne at 1 mM , Cs' at 45- 90 mM , and t et r odot oxi n at 10' . ( b) Subst ances t hat had a si gni fi cant i nhi bi t ory ef f ect on Na/ Ca exchange wer e: Mn 2+, Cd 2+, and Las" at 1- 50 mM , and qui ni di ne at 50 pM . ( c) Ther e wer e al so bl ocki ng agent s and bi ochem i cal i nhi bi t ors whose act i on appear ed to be t he i nhi bi ti on of nonm i t o- chondr i al Ca buf f er i ng in axopl asmr at her t han an i nhi bi ti on of Na/ Ca ex- change. These wer e t he gener al anest het i c 1- oct anol at 0.1 mMand 1 mM or t hovanadat e pl us apyr ase . I NTRODUCTI ON The pur pose of experi ment s r epor t ed her e was to exam i ne t he sensi t i vi t y of t he var i ous syst ems t hat al l ow Ca ent r y wi th depol ar i zat i on, as wel l as t hose buf f er i ng Ca i nt ernal l y in squi d gi ant axons, to a var i et y of chem i cal agent s t hat have been r epor t ed to i nf l uence Ca movement in cel l s . Si nce in many exci t abl e cel l s t her e ar e at l east t wo vol t age- sensi t i ve mechanisms t hat can al l ow Ca ent r y, t he Ca channel and Na/ Ca exchange, it is i mport ant to di st i ngui sh bet ween t hese t wo ent i t i es i n dr awi ng concl usi ons about t he ef f ect s Addr ess r epr i nt r equest s to Dr . L. J. Mullins, Dept . of Bi ophysi cs, Uni versi t y of Maryl and School of Medi ci ne, Bal ti more, MD21201 . J . GEN . PHYSTOL . © The Rockefel l er Uni versi t y Pr ess - 0022- 1295/ 85/ 06/ 0789/ 16 $1 . 00 789 Vol ume 85 June 1985 789- 804 on March 24, 2014 jgp.rupress.org Downloaded from Published June 1, 1985