The modulation of action potential generation by calcium-induced calcium release is enhanced by mitochondrial inhibitors in mudpuppy parasympathetic neurons.

Abstract Previously, we demonstrated that outward currents activated by calcium-induced calcium release (CICR) opposed depolarization-induced action potential (AP) generation in dissociated mudpuppy parasympathetic neurons [J Neurophysiol 88 (2002) 1119]. In the present study, we tested whether AP generation by depolarizing current ramps could be altered by dissipating the mitochondrial membrane potential and thus interrupting mitochondrial Ca 2+ buffering. Exposure to the protonophore carbonyl cyanide m -chlorophenylhydrazone (CCCP; 2 μM) alone or in combination with the mitochondrial ATP synthase inhibitor oligomycin (8 μg/ml), increased the latency to AP generation. Exposure to the electron transport chain inhibitor rotenone (10 μM) alone or in combination with oligomycin (8 μg/ml) similarly increased the latency to AP generation. CCCP and oligomycin or rotenone and oligomycin treatment caused rhodamine 123 loss from mitochondria within a few minutes, confirming that the mitochondrial membrane potential was dissipated during drug exposure. Oligomycin alone had no effect on the latency to AP generation and did not cause loss of rhodamine 123 from mitochondria. The increase in latency induced by CCCP and oligomycin was similar when recordings were made with either the perforated patch or standard whole cell patch recording configuration. Exposure to the endoplasmic reticulum Ca-ATPase inhibitor thapsigargin (1 μM), decreased the latency to AP generation. In cells pretreated with thapsigargin to eliminate CICR, CCCP and oligomycin had no effect on AP latency. Pretreatment with iberiotoxin (IBX; 100 nM), an inhibitor of large conductance, calcium- and voltage-activated potassium channels, reduced the extent of the CCCP- and oligomycin-induced increase in latency to AP generation. These results indicate that treatment with CCCP or rotenone to dissipate the mitochondrial membrane potential, a condition which should minimize sequestration of Ca 2+ by mitochondria, facilitated the Ca 2+ -induced Ca 2+ release activation of IBX-sensitive and IBX-insensitive conductances that regulate AP generation.