Hypoosmotic shock activates Ca2+ channels in isolated nerve terminals.
Influence of hypotonic swelling on Ca2+ (45Ca2+) uptake in rat brain synaptosomes was studied. A decrease in medium osmolality from 310 to 260-180 mOsm led to a progressive stimulation of 45Ca2+ accumulation. The effect was blocked by verapamil (IC50 = 5 microM), CoCl2 (IC50 = 58 microM) and retained at a fixed concentration of external sodium indicating the involvement of Ca2+ channels rather than Na+/Ca2+ exchange in swelling-induced Ca2+ influx. The populations of calcium channels observed in hypoosmotic and depolarizing conditions are different in three aspects: (i) kinetics of 45Ca2+ entry; (ii) insensitivity to dihydropyridines and omega-conotoxin GVIA; (iii) insensitivity to preliminary depolarization by high potassium. The effects of swelling and depolarization on Ca2+ uptake were additive. No change in membrane potential monitored with diS-C3-(5) was recorded during synaptosome hypotonic swelling. The results suggest the existence in synaptosomal plasma membrane of volume-dependent calcium-permeable channels with properties distinct from those of the voltage-dependent calcium channels. Activation of these channels may constitute an early event in volume regulation of nerve terminals in anisoosmotic conditions.
Mongin
A A
AA
Institute of Photobiology, Belarussian Academy of Sciences, Belarus. mongin@bas07.basnet.minsk.by
Aksentsev
S L
SL
Orlov
S N
SN
Konev
S V
SV
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D002132:Calcium Radioisotopes; D007038:Hypotonic Solutions / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009997:Osmotic Pressure; D051381:Rats; D017208:Rats, Wistar; D013574:Synaptosomes / Q000378:metabolism*
D015220:Calcium Channels; D002132:Calcium Radioisotopes; D007038:Hypotonic Solutions; D002118:Calcium