WATER BEFORE IONS? Early chill coma ion imbalance challenges the current mechanistic model of chill coma Lauren E. Des Marteaux & Brent J. Sinclair. University of Western Ontario. London, ON. Canada
Insect chill coma is associated with the loss of water & ion homeostasis
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Chill coma paralysis precedes hemolymph Hemolymph [K+] increases over the first 12 h of chill coma
• At their critical thermal minimum (CTmin) insects enter reversible paralysis (chill coma), during which they lose water and ion homeostasis.
+ K
imbalance
Muscle EK did not reach threshold values for paralysis before 12 h in chill coma
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I. ACTIVE TRANSPORT HYPOTHESIS Ion pumps fail at low temperatures, such that passive leak exceeds active transport
Hemolymph [K+] (mM)
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The current mechanistic model of chill coma:
Exposure to 0ºC (h)
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-1
24
0
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-35
20
12
PREDICTION: G. veletis avoids a loss of homeostasis at low temperatures by maintaining active transport that exceeds passive leak
K+
-45
8
-1
Na+
X
H2O
1.
[K+]
[K+]
1
2
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10 11 12 13
Exposure to 0ºC (h)
X
A linear increase in hemolymph [K+] over time at 0ºC was significant for both species (p = 5.8e-10 and 1.1e-6, respectively). N = 8 to 14 per time point per species.
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0
Muscle EK (mV)
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Muscle [K+] increases over the first 12 h of chill coma in G. veletis
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-50
Decreased hemolymph volume causes an increase in hemolymph [K+], leading to muscle depolarization (chill coma paralysis).
Hemolymph [Na+]
Hemolymph H2O volume
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40 60 80 Exposure to 0ºC (hr)
100
H2O
-60
-1
K+
0
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A linear increase in muscle [K+] over time at 0ºC was significant for G. veletis only (p=0.048). N = 11 to 13 per time point per species.
Hemolymph [Na+] (mM)
Hemolymph [Na+]
100
1
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6
0
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Contrary to predictions, hemolymph [Na+] rose to a peak at 1 h of exposure to 0ºC and then returned to ‘normal’ by 6 h. Gryllus veletis maintained lower hemolymph [Na+] in general.
The rise and fall of hemolymph Na+ content drives changes in hemolymph [Na+] 20
4. Water and ion balance calculations • Hemolymph and gut water volumes were used to calculate the hemolymph:gut water volume ratio.
Gut
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MacMillan & Sinclair. 2011. J. Exp. Biol. 214: 726-734
III. EPITHELIAL DAMAGE HYPOTHESIS Ionic and osmotic gradients are lost following leak of ions and water across a cold-damaged gut epithelium PREDICTION: G. veletis should exhibit structural modifications that prevent loss of gut epithelial integrity in the cold
IV. GRADIENT HYPOTHESIS Bulk movement of water and ions at low temperatures is driven by osmotic gradients across the gut PREDICTION: Bulk movement of water and ions at low temperatures can be mitigated by manipulating ionic and/or osmotic gradients between the gut and hemolymph
*
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Conclusions
Funding sources
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The patterns of water and ion imbalance in early chill coma do not support the current mechanistic model:
0.8 0.6
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– Chill coma paralysis does not result from K+ imbalance – Hemolymph [Na+] increases in early chill coma and therefore does not drive movement of water from hemolymph to gut
0.4
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-1 14
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10 11 12 13
Exposure to 0ºC (h)
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A linear decline in hemolymph : gut water volume ratio was observed over time at 0ºC in G. pennsylvanicus (p = 0.008) but not in G. veletis.
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Acknowledgements
* Gryllus veletis exhibited a lower water volume gradient between the hemolymph and gut at 25ºC (t = 3.7, df = 23, p
