Flufenamic acid affects multiple currents and causes intracellular Ca2+ release in Aplysia bag cell neurons.
Flufenamic acid (FFA) is a nonsteroidal antiinflammatory agent, commonly used to block nonselective cation channels. We previously reported that FFA potentiated, rather than inhibited, a cation current in Aplysia bag cell neurons. Prompted by this paradoxical result, the present study examined the effects of FFA on membrane currents and intracellular Ca2+ in cultured bag cell neurons. Under whole cell voltage clamp, FFA evoked either outward (I out) or inward (I in) currents. I out had a rapid onset, was inhibited by the K+ channel blocker, tetraethylammonium, and was associated with both an increase in membrane conductance and a negative shift in the whole cell current reversal potential. I in developed more slowly, was inhibited by the cation channel blocker, Gd3+, and was concomitant with both an increased conductance and positive shift in reversal potential. FFA also enhanced the use-dependent inactivation and caused a positive-shift in the activation curve of the voltage-dependent Ca2+ current. Furthermore, as measured by ratiometric imaging, FFA produced a rise in intracellular Ca2+ that persisted in the absence of extracellular Ca2+ and was reduced by depleting either the endoplasmic reticulum and/or mitochondrial stores. Ca2+ appeared to be involved in the activation of I in, as strong intracellular Ca2+ buffering effectively eliminated I in but did not alter I out. Finally, the effects of FFA were likely not due to block of cyclooxygenase given that the general cyclooxygenase inhibitor, indomethacin, failed to evoke either current. That FFA influences a number of neuronal properties needs to be taken into consideration when employing it as a cation channel antagonist.
Gardam
Kate E
KE
Department of Physiology and Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada.
Geiger
Julia E
JE
Hickey
Charlene M
CM
Hung
Anne Y
AY
Magoski
Neil S
NS
D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D001048:Aplysia / Q000166:cytology*; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation; D045604:Extracellular Fluid / Q000187:drug effects*; D005439:Flufenamic Acid / Q000494:pharmacology*; D016257:Fura-2 / Q000031:analogs & derivatives / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D009474:Neurons / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D019789:Tetraethylammonium / Q000494:pharmacology
D000893:Anti-Inflammatory Agents; D026902:Potassium Channel Blockers; C098106:fura-PE3; D005439:Flufenamic Acid; D019789:Tetraethylammonium; D002118:Calcium; D016257:Fura-2