[Characteristics of passive transport of 45Ca2(+) into the synaptosomes of the cerebral cortex in rats].
Transport of 45Ca2+ into synaptosomes was measured at 30 degrees C by rapid membrane filtration. The transport was saturable in high (135.10(-3) mol/l-1) or medium (25.10(-3) mol/l-1) K+ solutions with apparent KM values for 45Ca2+ of 0.45 and 0.1.10(-3) mol/l-1 respectively. At low K+ concentration (5.10(-3) mol/l-1) the transport was not clearly saturable by substrates. Vanadate had no effect on 45Ca2+ transport at any K+ concentration tested. Replacement of Na+ by other ions stimulated the 45Ca2+ transport with biphasic dependence on K+ concentration. Upon the substitution of choline for Na+, the dependence was monophasic and corresponded to Na/Ca antiporter reversal. The first stimulatory phase observed only in the presence of K+ corresponded to depolarization-activated transport. The phase itself occasionally showed a biphasic pattern with an extreme case of bell-shaped dependence on K+ concentration. The first phase set in immediately, whereas the onset of the second phase varied between the preparations. It could be shown that high K+ concentrations (as a rule approx. 50 mmol/l-1) may not be suitable for the study of depolarization-induced 45Ca2+ transport since they may induce NaůCa antiporter reversal. Also, it has been suggested that transport ATPases do not affect directly the basic parameters of passive 45Ca2+ transport into rat brain synaptosomes.
Orlický
J
J
Centra fyziologických vied SAV v Bratislave.
Varecka
L
L
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002132:Calcium Radioisotopes / Q000493:pharmacokinetics*; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism*; D066298:In Vitro Techniques; D051381:Rats; D012979:Sodium Radioisotopes / Q000493:pharmacokinetics; D013574:Synaptosomes / Q000378:metabolism*
D002132:Calcium Radioisotopes; D012979:Sodium Radioisotopes
Niektoré charakteristiky pasívneho transportu 45Ca2(+) do synaptozómov mozgovej kôry potkana.