Ba(2+)-induced chromaffin cell death: cytoprotection by Ca(2+) channel antagonists.
Exposure of bovine adrenal medullary chromaffin cells to Ba(2+) ions (in the absence of Ca(2+) ions) caused their death, measured as lactate dehydrogenase (LDH) release. The concentration of Ba(2+) required to damage the cells by about 65% ranged between 1 and 10 mM (no Ca(2+) added); the required exposure time was rather brief (15 min-4 h). The simultaneous presence of Ca(2+), Mg(2+) or Zn(2+) together with Ba(2+) (2 mM, 4 h) afforded cyprotection (60-80%). Individual selective blockers of Ca(2+) channel subtypes afforded no protection. However, combined nifedipine (3 microM) plus omega-conotoxin MVIIC (3 microM) offered full protection. Substantial protection was also seen with the "wide-spectrum" Ca(2+) channel blockers penfluridol (0.3 microM), lubeluzole (3 microM), dotarizine (3 microM), flunarizine (3 microM), and mibefradil (3 microM). This protection was due to blockade of Ba(2+) entry through Ca(2+) channels because dotarizine (10 microM) inhibited the increase in cytosolic [Ba(2+)] seen in fura-2-loaded chromaffin cells. Once Ba(2+) accumulated in the cytosol, it was not extruded by the Na(+)/Ca(2+) exchanger, as shown by the prolonged and sustained elevation of the fura-2 signal. This contrasts with the fast dissipation of the fura-2 signal generated by [Ca(2+)](i) elevation. Thus, Ba(2+) overload can cause cell death by mechanisms similar to those reported for Ca(2+) overload and might be used as a novel and convenient tool to search for new cytoprotective compounds.
Cano-Abad
M F
MF
Departamento de Farmacología, Instituto de Farmacología Teófilo Hernando, Facultad de Medicina, Universidad Autónoma de Madrid, C/ Arzobispo Morcillo, 4, E-28029, Madrid, Spain.
García
A G
AG
Sánchez-García
P
P
López
M G
MG
D000818:Animals; D001464:Barium / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000633:toxicity; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002413:Cations, Divalent / Q000494:pharmacology; D002417:Cattle; D016923:Cell Death / Q000187:drug effects; D019439:Chromaffin Cells / Q000187:drug effects* / Q000378:metabolism; D004396:Coloring Agents; D005456:Fluorescent Dyes; D016257:Fura-2; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D014343:Trypan Blue
D002121:Calcium Channel Blockers; D002413:Cations, Divalent; D004396:Coloring Agents; D005456:Fluorescent Dyes; D001464:Barium; D007770:L-Lactate Dehydrogenase; D014343:Trypan Blue; D016257:Fura-2