Protein kinase C (PKC) is an important
enzyme involved in the regulation of neurotransmission and might also be important in the mediation of ischemic neuronal death. PKC has been implicated as a target of volatile
anesthetics as well as in
anesthetic protection against
ischemia. The present study tested the effect of
isoflurane and
sevoflurane, both used in neuroanesthetic practice, on presynaptic free cytosolic Ca2+ ([Ca2+](i)) and PKC activity. To measure [Ca2+](i) and PKC activation simultaneously, rat synaptosomes, mostly containing presynaptic terminals, were loaded with the
fluorescent probes fura-2 and
fim-1, respectively. The synaptosomes were exposed to either
isoflurane or
sevoflurane in concentrations corresponding to 1 and 2 MAC values in rats, both in Ca2+-containing and Ca2+-free medium. After 8 minutes of
anesthetic exposure, 1 mM
4-aminopyridine was added to induce membrane depolarization.
Isoflurane 1 and 2 MAC increased the basal PKC activity after 8 minutes in Ca2+-containing medium by 15.1% (3.6%) and 30.5% (5.5%) compared with control, respectively [mean (SEM); n = 9, both values P < 0.05].
Sevoflurane 2 MAC transiently decreased but thereafter increased the PKC activity (P < 0.05). In Ca2+ -free medium
sevoflurane attenuated the PKC activity (P < 0.05). The
anesthetics did not alter the depolarization-evoked enzyme activation. Furthermore, 2 MAC of both
isoflurane and
sevoflurane increased the basal- and attenuated the depolarization-evoked increase in [Ca2+](i) (P < 0.05). The present study supports the hypotheses that volatile
anesthetics affect presynaptic PKC activity and that the
anesthetic effect on enzyme activation seems to be related to an increase in [Ca2+](i).