Non-uniform Ca²⁺ buffer distribution in a nerve cell body

Abstract

In nerve cells, Ca²⁺ influx through voltage-dependent channels in the membrane causes a transient rise in the intracellular, free Ca²⁺ concentration^1–3. Such changes have been shown to be important for the release of transmitter at the axon terminal^3,4 and for the control of the movement of ions through channels in the soma membrane^5,6. The transient behaviour of the rise in Ca²⁺ concentration can, in part, be explained by the presence of sequestering systems in the cell which tend to limit the magnitude and duration of changes in internal Ca²⁺ (refs 7–10). It is possible that systems involved in buffering changes in internal Ca²⁺ are not distributed uniformly throughout the cell. This is particularly likely in the cell body, where a significant portion of the cytoplasm is occupied by the nucleus, whose buffering capacity may differ from that of other cellular regions. We report here that in the soma of a molluscan pacemaker neurone, the machinery responsible for short-term buffering of Ca²⁺ ions is localized near the inner surface of the plasma membrane.