Changes in free-calcium levels and pH in synaptosomes during transmitter release.
The free cytoplasmic Ca2+ concentration [( Ca2+]i) in rat brain synaptosomes estimated by the indicator quin 2 is 104 +/- 8 nM (S.D.) in artificial cerebrospinal fluid (1.2 mM Ca2+), but decreases at lower Ca2+ concentrations in the medium. The presence of quin 2 in the synaptosomes does not affect either the spontaneous release of transmitter (gamma-aminobutyric acid) or the release induced by K+ depolarisation. In quin 2-loaded synaptosomes, depolarisation by K+ causes an abrupt increase in [Ca]i (less than 2-fold) that is approximately proportional to the extent of depolarisation, whereas depolarisation by veratrine alkaloids produces a slow rise in [Ca]i. The increase in [Ca]i produced by K+ depolarisation does not occur in the absence of Ca2+ in the medium. The data are consistent with a direct correlation between [Cai] and transmitter release in functional synaptosomes. The pH in synaptosomes estimated by the indicator quene 1 is 7.04 +/- 0.07 and is stable in media containing 5 mM bicarbonate. The pH in synaptosomes was decreased by protoveratrine but not by K+ depolarisation.
D000634:Aminoquinolines; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013050:Spectrometry, Fluorescence; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D000634:Aminoquinolines; D002121:Calcium Channel Blockers; D005456:Fluorescent Dyes; D005680:gamma-Aminobutyric Acid; C035739:Quin2; D011188:Potassium; D002118:Calcium