Published in:
The Journal of Physiology, 582 (2007) 1, Seite 163-175
Language:
English
DOI:
10.1113/jphysiol.2006.125963
ISSN:
0022-3751;
1469-7793
Origination:
Footnote:
Description:
Multi‐neuronal recordings with Ca2+ indicator dyes usually relate [Ca2+]i to action potentials (APs) assuming a stereotypical dependency between the two. However, [Ca2+]i affects and is affected by numerous complex mechanisms that differ from cell type to cell type, from cell compartment to cell compartment. Moreover, [Ca2+]i depends on the specific way a cell is activated. Here we investigate, by combining calcium imaging and on‐cell patch clamp recordings, the relationship between APs (spiking) and somatic [Ca2+]i in mitral and granule cells of the olfactory bulb in Xenopus laevis tadpoles. Both cell types exhibit ongoing and odour‐modulated [Ca2+]i dynamics. In mitral cells, the occurrence of APs in both spontaneous and odour‐evoked situations correlates tightly to step‐like [Ca2+]i increases. Moreover, odorant‐induced suppression of spontaneous firing couples to a decrease in [Ca2+]i. In contrast, granule cells show a substantial number of uncorrelated events such as increases in [Ca2+]i without APs occurring or APs without any effect upon [Ca2+]i. The correlation between spiking and [Ca2+]i is low, possibly due to somatic NMDAR‐mediated and subthreshold voltage‐activated Ca2+ entries, and thus does not allow a reliable prediction of APs based on calcium imaging. Taken together, our results demonstrate that the relationship between somatic [Ca2+]i and APs can be cell type specific. Taking [Ca2+]i dynamics as an indicator for spiking activity is thus only reliable if the correlation has been established in the system of interest. When [Ca2+]i and APs are precisely correlated, fast calcium imaging is an extremely valuable tool for determining spatiotemporal patterns of APs in neuronal population.