Decreased calcium accumulation in isolated nerve endings during hibernation in ground squirrels.
Resting and depolarization-induced 45CaCl2 accumulation was compared for synaptosomes isolated from hibernating and nonhibernating ground squirrels. Channel subtype antagonists were used to identify the active voltage-sensitive calcium channel subtypes in these preparations. There was significantly less 45Ca2+ accumulation in synaptosomes isolated from hibernating as compared to cold-adapted nonhibernating ground squirrels in both basal (p < 0.005) and depolarizing (p < 0.03) media over a 30 sec to 5 min incubation period. The elevation in 45Ca2+ accumulation triggered by K+ depolarization was blocked by 50 microM CdCl2, 1 microM omega-conotoxin MVIIC or 1 microM omega-agatoxin IVA. Inhibition was not observed with 1 microM nifedipine or with 1 microM omega-conotoxin GVIA. These results suggest that hibernation is associated with reduced presynaptic 45Ca2+ conductance via voltage-sensitive channels with a pharmacological sensitivity that is different from the established L-, N-, and P-types in other systems but share features of the recently described Q-type calcium channel. This decrease may reflect a cellular adaptation that helps confer tolerance to the near total cerebral ischemia associated with hibernation.
Stroke Branch, NINDS, National Institutes of Health, Bethesda, Maryland 20892-4128, USA.
N T
NT
Gentile
M
M
Spatz
M
M
Brenner
R M
RM
McCarron
J M
JM
Hallenbeck
D000110:Acetylcholinesterase / Q000378:metabolism; D000704:Analysis of Variance; D000818:Animals; D001143:Arousal; D001921:Brain / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002458:Cell Fractionation; D006605:Hibernation; D008928:Mitochondria / Q000502:physiology; D009411:Nerve Endings / Q000502:physiology*; D012589:Sciuridae / Q000502:physiology*; D013574:Synaptosomes / Q000187:drug effects / Q000502:physiology*
D002121:Calcium Channel Blockers; D000110:Acetylcholinesterase; D002118:Calcium