Depolarization-induced increase in synaptosomal membrane calcium monitored by chlorotetracycline fluorescence.
Chlorotetracycline (CT) was used as a fluorescent probe for membrane calcium with intact synaptosomes. The net increase in fluorescence intensity at 520 nm, which is a measure of membrane-bound Ca, increases with increasing Ca, saturating in the millimolar range. Membrane Ca can also be detected in the absence of added external Ca. Potassium-induced depolarization of synaptosomes leads to an increase in membrane Ca, reaching a new steady-state value within 5 min. Neither opiates nor phenytoin affected synaptosomal membrane Ca. Relatively high concentrations of chlorotetracycline increased depolarization-induced uptake of 45Ca into synaptosomes. The data suggest that the Ca-CT complex binds to synaptic plasma membranes, and that depolarization-induced Ca influx results in increased Ca binding to the internal surface of the plasma membrane and/or other internal membranes.
D000818:Animals; D001921:Brain / Q000502:physiology; D002118:Calcium / Q000502:physiology*; D002751:Chlortetracycline; D008564:Membrane Potentials; D010741:Phospholipases A / Q000378:metabolism; D051381:Rats; D013050:Spectrometry, Fluorescence; D013574:Synaptosomes / Q000502:physiology*
D010741:Phospholipases A; D002118:Calcium; D002751:Chlortetracycline