Spatiotemporal Distribution of Ca2+ Following Axotomy and Throughout the Recovery Process of Cultured Aplysia Neurons

Noam E. Ziv, Micha E. Spira*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

81 Scopus citations

Abstract

This study investigates the alterations in the spatiotemporal distribution pattern of the free intracellular Ca2+ concentration ([Ca2+]i) during axotomy and throughout the recovery process of cultured Aplysia neurons, and correlates these alterations with changes in the neurons input resistance and trans‐membrane potential. For the experiments, the axons were transected while imaging the changes in [Ca2+]i with fura‐2, and monitoring the neurons’resting potential and input resistance (Ri) with an intracellular microelectrode inserted into the cell body. The alterations in the spatiotemporal distribution pattern of [Ca2+]i were essentially the same in the proximal and the distal segments, and occurred in two distinct steps: concomitantly with the rupturing of the axolemma, as evidenced by membrane depolarization and a decrease in the input resistance, [Ca2+]i increased from resting levels of 0.05 – 0.1 μM to 1 – 1.5 μM along the entire axon. This is followed by a slower process in which a [Ca2+]i front propagates at a rate of 11 – 16 μm/s from the point of transection towards the intact ends, elevating [Ca2+]i to 3 – 18 μM. Following the resealing of the cut end 0.5 – 2 min post‐axotomy, [Ca2+]i recovers in a typical pattern of a retreating front, travelling from the intact ends towards the cut regions. The [Ca2+]i recovers to the control level 7 – 10 min post‐axotomy. In Ca2+‐free artificial sea water (2.5 mM EGTA) axotomy does not lead to increased [Ca2+]i and a membrane seal is not formed over the cut end. Upon reperfusion with normal artificial sea water, [Ca2+]i is elevated at the tip of the cut axon and a membrane seal is formed. This experiment, together with the observations that injections of Ca2+, Mg2+ and Na+ into intact axons do not induce the release of Ca2+ from intracellular stores, indicates that Ca2+ influx through voltage gated Ca2+ channels and through the cut end are the primary sources of [Ca2+]i following axotomy. However, examination of the spatiotemporal distribution pattern of [Ca2+]i following axotomy and during the recovery process indicates that diffusion is not the dominating process in shaping the [Ca2+]i gradients. Other Ca2+ regulatory mechanisms seem to be very effective in limiting these gradients, thus enabling the neuron to survive the injury.

Original languageEnglish
Pages (from-to)657-668
Number of pages12
JournalEuropean Journal of Neuroscience
Volume5
Issue number6
DOIs
StatePublished - Jun 1993

Keywords

  • cultured neurons
  • free calcium
  • fura‐2
  • nerve injury

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