Calcium homeostasis in rat septal neurons in tissue culture

David Bleakman, John D. Roback, Bruce H. Wainer, Richard J. Miller, Neil L. Harrison*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

62 Scopus citations

Abstract

Septal neutons from embryonic rats were grown in tissue culture. Microfluorimetric and electrophysiological techniques were used to study Ca2+ homeostasis in these neurons. The estimated basal intracellular free ionized calcium concentration ([Ca2+]i) in the neurons was low (50-100 nM). Depolarization of the neurons with 50 mM K+ resulted in rapid elevation of [Ca2+]i to 500-1,000 nM showing recovery to baseline [Ca2+]i over several minutes. The increases in [Ca2+]i caused by K+ depolarization were completely abolished by the removal of extracellular [Ca2+], and were reduced by ∼80% by the 'L-type' Ca2+ channel blocker, nimodipine (1 μM). [Ca2+]i was also increased by the excitatory amino and l-glutamate, quisqualate, AMPA and kainate. Responses to AMPA and kainate were blocked by CNOX and DNOX. In the absence of extracellular Mg2+, large fluctuations in [Ca2+]i were observed that were blocked by removal of extracellular Ca2+, by tetrodotoxin (TTX), or by antagonists of N-methyl d-aspartate (NMDA) such as 2-amino 5-phosphonovalerate (APV). In zero Mg2+ and TTX, NMDA caused dose-dependent increases in [Ca2+]i that were blocked by APV. Caffeine (10 mM) caused transient increases in [Ca2+]i in the absence of extracellular Ca2+, which were prevented by thapsigargin, suggesting the existence of caffeine-sensitive ATP-dependent intracellular Ca2+ stores. Thapsigargin (2 μM) had little effect on [Ca2+]i, or on the recovery from K+ depolarization. Removal of extracellular Na+ had little effect on basal [Ca2+]i or on responses to high K+, suggesting that Na+/Ca2+ exchange mechanisms do not play a significant role in the short-term control of [Ca2+]i in septal neurons. The mitochondrial uncoupler, CCCP, caused a slowly developing increase in basal [Ca2+]i; however, [Ca2+]i recovered as normal from high K+ stimulation in the presence of CCCP, which suggests that the mitochondria are not involved in the rapid buffering of moderate increases in [Ca2+]i. In simultaneous electrophysiological and microfluorimetric recordings, the increase in [Ca2+]i associated with action potential activity was measured. The amplitude of the [Ca2+]i increase induced by a train of action potentials increased with the duration of the train, and with the frequency of firing, over a range of frequencies between 5 and 200 Hz. Recovery of [Ca2+]i from the modest Ca2+ loads imposed on the neuron by action potential trains follows a simple exponential decay (τ = 3-5 s).

Original languageEnglish (US)
Pages (from-to)257-267
Number of pages11
JournalBrain research
Volume600
Issue number2
DOIs
StatePublished - Jan 15 1993

Keywords

  • Calcium channel
  • Frequency
  • Fura-2
  • Mitochondria

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Clinical Neurology
  • Developmental Biology

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