Effects of dotarizine and flunarizine on chromaffin cell viability and cytosolic Ca 2+

Abstract

Dotarizine (a novel piperazine derivative with antimigraine properties) and flunarizine (a Ca 2+ channel antagonist) were compared concerning: first, their ability to cause chromaffin cell damage in vitro; second, the possible correlation of their octanol/water partition coefficients and those of another 28 compounds (i.e., Ca 2+ channel antagonists, blockers of histamine H 1 receptors, antimycotics, β-adrenoceptor antagonists, neuroleptics), with their ability to cause cell damage; third, their capacity to protect the cells against the damaging effects of veratridine; and fourth, their capabilities to enhance the basal cytosolic Ca 2+ concentration in fura-2-loaded single chromaffin cells, or to modify the pattern of [Ca 2+] i oscillations elicited by veratridine. After 24-h exposure to 1–30 μM dotarizine, the viability of bovine adrenal chromaffin cells (measured under phase contrast or as lactate dehydrogenase, released into the medium) was similar to that of control, untreated cells; at 100 μM, 80% lactate dehydrogenase release was produced. At 1–3 μM flunarizine caused no cell damage; however 10 μM caused 20% lactate dehydrogenase release and 30 and 100 μM over 90% lactate dehydrogenase release. The time course of cell damage was considerably faster for flunarizine, in comparison to dotarizine. Out of 30 molecules tested (at 10 μM), having different octanol/water partition coefficients (log P), dotarizine was among the molecules causing no cell damage; flunarizine caused 20% cell loss, lidoflazine and verapamil over 50% cell loss, and penfluridol, draflazine, astemizole or nifedipine over 80% cell loss. No correlation was found between log P and cytotoxicity. Both dotarizine (10–30 μM) and flunarizine (3–10 μM) provided protection against veratridine-induced cell death; however, at 30 μM dotarizine afforded a pronounced protection while flunarizine enhanced the cytotoxic effects of veratridine. Dotarizine (30 μM) (but not flunarizine) caused a prompt transient elevation of the basal [Ca 2+] i. Both compounds abolished the K +-induced increases of [Ca 2+] i as well as the oscillations of [Ca 2+] i induced by veratridine. The blocking effects of dotarizine were readily reversed after washout, while those of flunarizine were long-lasting. These differences might be relevant to the clinical use of dotarizine as an antimigraine drug.