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. 2009 Aug 25;4(8):e6742.
doi: 10.1371/journal.pone.0006742.

Correlations in Ion Channel mRNA in Rhythmically Active Neurons

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Free PMC article

Correlations in Ion Channel mRNA in Rhythmically Active Neurons

Anne-Elise Tobin et al. PLoS One. .
Free PMC article

Abstract

Background: To what extent do identified neurons from different animals vary in their expression of ion channel genes? In neurons of the same type, is ion channel expression highly variable and/or is there any relationship between ion channel expression that is conserved?

Methodology/principal findings: To address these questions we measured ion channel mRNA in large cells (LCs) of the crab cardiac ganglion. We cloned a calcium channel, caco, and a potassium channel, shaker. Using single-cell quantitative PCR, we measured levels of mRNA for these and 6 other different ion channels in cardiac ganglion LCs. Across the population of LCs we measured 3-9 fold ranges of mRNA levels, and we found correlations in the expression of many pairs of conductances

Conclusions/significance: In previous measurements from the crab stomatogastric ganglion (STG), ion channel expression was variable, but many pairs of channels had correlated expression. However, each STG cell type had a unique combination of ion channel correlations. Our findings from the crab cardiac ganglion are similar, but the correlations in the LCs are different from those in STG neurons, supporting the idea that such correlations could be markers of cell identity or activity.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Spontaneous activity of the cardiac ganglion in C. borealis.
Top: intracellular recording from the axon of a LC. Bottom: simultaneous extracellular recording from the cardiac ganglion trunk, showing small cell (small units) and large cell (LC) (tall units) bursts of action potentials.
Figure 2
Figure 2. Mean mRNA copy numbers for 8 ion channel gene transcripts in LCs.
The LC groups were harvested and processed at different times during the year. The numbers of cells included in each analysis (n) are indicated inside or above standard deviation bars. Asterisks indicate significance differences at p<0.01 (*) or p<0.001 (***) for the same channel between two groups of cells (t-test).
Figure 3
Figure 3. Example ion channel mRNA profiles from 3 groups of LCs.
All cells in each group are processed together; these LCs were randomly selected among the cells with measurements for each transcript.
Figure 4
Figure 4. Ion channel mRNA measurements are not apparently more similar within an animal than across the population.
For several example channels, measured in Group 1 LCs, there is no clear indication of clustering of ion channel measurements within an animal. There are no significant differences in channel mRNA levels between anterior (ant.) and posterior (post.) LCs (as determined by t-tests). Note that in ganglia where fewer than 5 LCs are shown, levels may artificially appear less variable.
Figure 5
Figure 5. Levels of mRNA for 6 pairs of ion channels show significant strong (R2>0.6) positive correlations.
Top: (left to right): shaker (IA) correlates with BKKCa (IKCa) in Group 3, shab (IKd) correlates with caco (ICa) in Group 1, shab correlates with para (INa) in Group 2. Bottom: (left to right): caco, shaker, and shal (IA) correlate with para in Group 3. For para vs. shaker, data and correlations are shown also for Group 2 (white squares).

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