Ca2+-Dependent, Stimulus-Specific Modulation of the Plasma Membrane Ca2+ Pump in Hippocampal Neurons

Ferragamo MJ, Reinardy JL, Thayer SA. Ca2+-dependent, stimulus-specific modulation of the plasma membrane Ca2+ pump in hippocampal neurons. J Neurophysiol 101: 2563-2571, 2009. First published February 25, 2009; doi:10.1152/jn.90774.2008. The plasma membrane Ca2+ ATPase (PMCA) plays a major role in restoring Ca2+ to basal levels following transient elevation by neuronal activity. Here we examined the effects of various stimuli that increase [Ca2+](i) on PMCA-mediated Ca2+ clearance from hippocampal neurons. We used indo-1-based microfluorimetry in the presence of cyclopiazonic acid to study the rate of PMCA-mediated recovery of Ca2+ elevated by a brief train of action potentials. [Ca2+](i) recovery was described by an exponential decay and the time constant provided an index of PMCA-mediated Ca2+ clearance. PMCA function was assessed before and for >= 60 min following a 10-min priming stimulus of either 100 mu M N-methyl-D-aspartate (NMDA), 0.1 mM Mg2+ (reduced extracellular Mg2+ induces intense excitatory synaptic activity), 30 mM K+, or control buffer. Recovery kinetics slowed progressively following priming with NMDA or 0.1 mM Mg2+; in contrast, Ca2+ clearance initially accelerated and then slowly returned to initial rates following priming with 30 mM K+-induced depolarization. Treatment with 10 mu M calpeptin, an inhibitor of the Ca2+ activated protease calpain, prevented the slowing of kinetics observed following treatment with NMDA but had no affect on the recovery kinetics of control cells. Calpeptin also blocked the rapid acceleration of Ca2+ clearance following depolarization. In calpeptin-treated cells, 0.1 mM Mg2+ induced a graded acceleration of Ca2+ clearance. Thus in spite of producing comparable increases in [Ca2+](i), activation of NMDA receptors, depolarization-induced activation of voltage-gated Ca2+ channels and excitatory synaptic activity each uniquely affected Ca2+ clearance kinetics mediated by the PMCA.