Synaptosomal plasma membrane Ca(2+) pump activity inhibition by repetitive micromolar ONOO(-) pulses.
A sustained increase of intracellular free [Ca(2+)] ([Ca(2+)](i)) has been shown to be an early event of neuronal cell death induced by peroxynitrite (ONOO(-)). In this paper, chronic exposure to ONOO(-) has been simulated by treatment of rat brain synaptosomes or plasma membrane vesicles with repetitive pulses of ONOO(-) during at most 50 min, which efficiently produced nitrotyrosine formation in several membrane proteins (including the Ca(2+)-ATPase). The plasma membrane Ca(2+)-ATPase activity at near-physiological conditions (pH 7, submicromolar Ca(2+), and millimolar Mg(2+)-ATP concentrations), which plays a major role in the control of synaptic [Ca(2+)](i), can be more than 75% inhibited by a sustained exposure to micromolar ONOO(-) (e.g., to 100 pulses of 10 microM ONOO(-)). This inhibition is irreversible and mostly due to a decreased V(max), and to the 2-fold increase of the K(0.5) for Ca(2+) stimulation and about 5-fold increase of the K(M) for Mg(2+)-ATP. [Ca(2+)](i) increases to >400 nM when synaptosomes are subjected to this treatment. Reduced glutathione can afford only partial protection against the inhibition produced by micromolar ONOO(-) pulses. Therefore, inhibition of the plasma membrane Ca(2+)-pump activity during chronic exposure to ONOO(-) may account by itself for a large and sustained increase of intracellular [Ca(2+)](i) in synaptic nerve terminals.
Gutiérrez-Martín
Yolanda
Y
Departamento de Bioquímica y Biología Molecular y Genética, Facultad de Ciencias, Universidad de Extremadura, Avenida de Elvas s/n 06080-Badajoz, Spain.
Martín-Romero
Francisco Javier
FJ
Henao
Fernando
F
Gutiérrez-Merino
Carlos
C
D000818:Animals; D001921:Brain / Q000166:cytology / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004795:Enzyme Stability / Q000187:drug effects / Q000502:physiology; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology; D030421:Peroxynitrous Acid / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
D030421:Peroxynitrous Acid; D014443:Tyrosine; D000252:Calcium-Transporting ATPases; D002118:Calcium