Premium
Effect of Monovalent Cations on Na + /Ca 2+ Exchange and ATP‐Dependent Ca 2+ Transport in Synaptic Plasma Membranes
Author(s) -
Coutinho O. P.,
Carvalho A. P.,
Carvalho C. A. M.
Publication year - 1983
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1983.tb04793.x
Subject(s) - chemistry , vesicle , membrane , sodium , biophysics , membrane transport , synaptic vesicle , choline , calcium , biochemistry , biology , organic chemistry
Two Ca 2+ transport systems were investigated in plasma membrane vesicles isolated from sheep brain cortex synaptosomes by hypotonic lysis and partial purification. Synaptic plasma membrane vesicles loaded with Na + (Na + i ) accumulate Ca 2+ in exchange for Na + , provided that a Na + gradient (in→out) is present. Agents that dissipate the Na + gradient (monensin) prevent the Na + /Ca 2+ exchange completely. Ca 2+ accumulated by Na + /Ca 2+ exchange can be released by A 23187, indicating that Ca 2+ is accumulated intravesicularly. In the absence of any Na + gradient (K + i ‐loaded vesicles), the membrane vesicles also accumulate Ca 2+ owing to ATP hydrolysis. Monovalent cations stimulate Na + /Ca 2+ exchange as well as the ATP‐dependent Ca 2+ uptake activity. Taking the value for Na + /Ca 2+ exchange in the presence of choline chloride (external cation) as reference, other monovalent cations in the external media have the following effects: K + or NH 4 + stimulates Na + /Ca 2+ exchange; Li + or Cs + inhibits Na + /Ca 2+ exchange. The ATP‐dependent Ca 2+ transport system is stimulated by increasing K + concentrations in the external medium ( K m for K + is 15 m M ). Replacing K + by Na + in the external medium inhibits the ATP‐dependent Ca 2+ uptake, and this effect is due more to the reduction of K + than to the elevation of Na + . The results suggest that synaptic membrane vesicles isolated from sheep brain cortex synaptosomes possess mechanisms for Na + /Ca 2+ exchange and ATP‐dependent Ca 2+ uptake, whose activity may be regulated by monovalent cations, specifically K + , at physiological concentrations.