[Calcium transport in brain synaptosomes during depolarization. The role of potential-dependent channels and Na+/Ca2+ metabolism].
The contribution of Ca2+ channels and Na+/Ca2+ exchange to Ca2+ uptake in rat brain synaptosomes upon long- (t greater than or equal to 30 s) and short-term (t less than 30 s) depolarization by high K+ was studied by measuring the 45Ca content and free Ca2+ concentration (from Quin-2 fluorescence). At 37 degrees C, the system responsible for the K+-stimulated uptake of 45Ca (t greater than or equal to 30 s) and the Na+/Ca+ exchanger are characterized by a similar concentration dependence of external Ca2+ (Ca0(2+] and K0+ as well as by an equal sensitivity to verapamil (Ki = approximately 20-40 microM) and La2+ (Ki = approximately 50 microM). These data and the results from predepolarization suggest that the 45Ca entry into synaptosomes at t greater than or equal to 30 s is due to the activation of Na+/Ca+ exchange caused by its electrogenic component, while the insignificant contribution of Ca2+ channels can be accounted for by their inactivation. At low temperatures (2-4 degrees C) which decelerate the inactivation, the initial phase of 45Ca uptake is fully provided for by Ca2+ channels, showing a lower (as compared to the exchanger) affinity for Ca0(2+) (K0.5 greater than 1 mM)m a greater sensitivity to La3+ (Ki = approximately 0.2-0.3 microM) and verapamil (Ki = approximately 2-3 microM); these channels are fully inactivated by predepolarization with K0+, ouabain and batrachotoxin. The Ca2+ channels can be related to T-type channels, since they are not blocked by nicardipine and niphedipine.
Konev
S V
SV
Aksentsev
S L
SL
Okun'
I M
IM
Merezhinskaia
N V
NV
Rakovich
A A
AA
Orlov
S N
SN
Pokudin
N I
NI
Kravtsov
G M
GM
Khodorov
B I
BI
D000818:Animals; D001496:Batrachotoxins / Q000494:pharmacology; D001692:Biological Transport; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D011921:Rats, Inbred WKY; D012964:Sodium / Q000378:metabolism*; D013574:Synaptosomes / Q000378:metabolism*
D001496:Batrachotoxins; D015220:Calcium Channels; D010042:Ouabain; D012964:Sodium; D002118:Calcium
Transport kal'tsiia v sinaptosomakh mozga pri depoliarizatsii. Rol' potentsialzavisimykh kanalov i Na+/Ca2+-obmena.