CICR
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 microM) alone or in combination with the mitochondrial ATP synthase inhibitor oligomycin (8 microg/ml), increased the latency to AP generation.
Exposure to the electron transport chain inhibitor rotenone (10 microM) alone or in combination with oligomycin
(8 microg/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 microM),
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.
PMID: 14980383 [PubMed - in process]