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Upregulation of T-type Ca2+ channels in long-term diabetes determines increased excitability of a specific type of capsaicin-insensitive DRG neurons.

Duzhyy DE, Viatchenko-Karpinski VY, Khomula EV, Voitenko NV, Belan PV - Mol Pain (2015)

Bottom Line: This upregulation was not accompanied by significant changes in biophysical properties of T-type channels suggesting that a density of functionally active channels was increased.The upregulation of T-type channels resulted in the increased neuronal excitability of these nociceptive neurons revealed by a lower threshold for action potential initiation, prominent afterdepolarizing potentials and burst firing.Capsaicin-insensitive low-pH-sensitive type of DRG neurons shows diabetes-induced upregulation of Cav3.2 subtype of T-type channels.

View Article: PubMed Central - PubMed

Affiliation: Department of General Physiology of the CNS and State Key Laboratory of Molecular and Cellular Biology, Bogomoletz Institute of Physiology of National Academy of Science of Ukraine, 4 Bogomoletz street, 01024, Kyiv, Ukraine. dduzhyy@biph.kiev.ua.

ABSTRACT

Background: Previous studies have shown that increased excitability of capsaicin-sensitive DRG neurons and thermal hyperalgesia in rats with short-term (2-4 weeks) streptozotocin-induced diabetes is mediated by upregulation of T-type Ca(2+) current. In longer-term diabetes (after the 8th week) thermal hyperalgesia is changed to hypoalgesia that is accompanied by downregulation of T-type current in capsaicin-sensitive small-sized nociceptors. At the same time pain symptoms of diabetic neuropathy other than thermal persist in STZ-diabetic animals and patients during progression of diabetes into later stages suggesting that other types of DRG neurons may be sensitized and contribute to pain. In this study, we examined functional expression of T-type Ca(2+) channels in capsaicin-insensitive DRG neurons and excitability of these neurons in longer-term diabetic rats and in thermally hypoalgesic diabetic rats.

Results: Here we have demonstrated that in STZ-diabetes T-type current was upregulated in capsaicin-insensitive low-pH-sensitive small-sized nociceptive DRG neurons of longer-term diabetic rats and thermally hypoalgesic diabetic rats. This upregulation was not accompanied by significant changes in biophysical properties of T-type channels suggesting that a density of functionally active channels was increased. Sensitivity of T-type current to amiloride (1 mM) and low concentration of Ni(2+) (50 μM) implicates prevalence of Cav3.2 subtype of T-type channels in the capsaicin-insensitive low-pH-sensitive neurons of both naïve and diabetic rats. The upregulation of T-type channels resulted in the increased neuronal excitability of these nociceptive neurons revealed by a lower threshold for action potential initiation, prominent afterdepolarizing potentials and burst firing. Sodium current was not significantly changed in these neurons during long-term diabetes and could not contribute to the diabetes-induced increase of neuronal excitability.

Conclusions: Capsaicin-insensitive low-pH-sensitive type of DRG neurons shows diabetes-induced upregulation of Cav3.2 subtype of T-type channels. This upregulation results in the increased excitability of these neurons and may contribute to nonthermal nociception at a later-stage diabetes.

No MeSH data available.


Related in: MedlinePlus

Diabetic-induced changes of the AP parameters for the caps−lpH+ neurons reflect increased excitability of these neurons in diabetes. a A representative AP trace with a slight AHP recorded from the caps−lpH+ neuron of normal rat. b A representative AP trace with a substantial ADP recorded from the caps−lpH+ neuron of diabetic rat. c The ADP/AHP area is significantly increased in diabetes compared to control indicating an increase in excitability of the caps−lpH+ neurons including probability of their bursting in diabetic conditions. Numbers of cells: control for diabetes n = 20 from four rats, diabetes n = 28 from four rats, p < 0.05. d A representative trace of AP bursts generated in 25 % of diabetic neurons (n = 28 from four rats) at a threshold current stimulation. At the same time no AP bursts were observed in the caps−lpH+ neurons of control rats (n = 20 from four rats). e Application of amiloride converts ADPs (top left) and bursts (bottom left) observed in the diabetic caps−lpH+ neurons to AHPs (top and bottom right). f Diabetes leads to a statistically significant decrease in the AP threshold. Numbers of cells: control for diabetes n = 20 from four rats, diabetes n = 28 from four rats, p < 0.05
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Fig6: Diabetic-induced changes of the AP parameters for the caps−lpH+ neurons reflect increased excitability of these neurons in diabetes. a A representative AP trace with a slight AHP recorded from the caps−lpH+ neuron of normal rat. b A representative AP trace with a substantial ADP recorded from the caps−lpH+ neuron of diabetic rat. c The ADP/AHP area is significantly increased in diabetes compared to control indicating an increase in excitability of the caps−lpH+ neurons including probability of their bursting in diabetic conditions. Numbers of cells: control for diabetes n = 20 from four rats, diabetes n = 28 from four rats, p < 0.05. d A representative trace of AP bursts generated in 25 % of diabetic neurons (n = 28 from four rats) at a threshold current stimulation. At the same time no AP bursts were observed in the caps−lpH+ neurons of control rats (n = 20 from four rats). e Application of amiloride converts ADPs (top left) and bursts (bottom left) observed in the diabetic caps−lpH+ neurons to AHPs (top and bottom right). f Diabetes leads to a statistically significant decrease in the AP threshold. Numbers of cells: control for diabetes n = 20 from four rats, diabetes n = 28 from four rats, p < 0.05

Mentions: Correlation between the ADP/AHP area or the AP threshold and T-type current density was also directly established for the caps−lpH+ neurons (Fig 5) by measuring AP parameters and TCD for the same neuron in Tyrode’s and TEA-Cl, Ba2+-based solutions, respectively. Fig 6 clearly demonstrates a robust correlation between TCD and AP parameters characterizing neuronal excitability. Corresponding Pearson correlation coefficient and level of significance for correlation of the ADP/AHP area and the AP threshold with the TCD were 0.78, p < 1*E−5 and 0.7, p < 0.002, respectively. Thus, T-type current in the caps−lpH+ neurons is significantly correlated with the neuronal excitability parameters.Fig. 6


Upregulation of T-type Ca2+ channels in long-term diabetes determines increased excitability of a specific type of capsaicin-insensitive DRG neurons.

Duzhyy DE, Viatchenko-Karpinski VY, Khomula EV, Voitenko NV, Belan PV - Mol Pain (2015)

Diabetic-induced changes of the AP parameters for the caps−lpH+ neurons reflect increased excitability of these neurons in diabetes. a A representative AP trace with a slight AHP recorded from the caps−lpH+ neuron of normal rat. b A representative AP trace with a substantial ADP recorded from the caps−lpH+ neuron of diabetic rat. c The ADP/AHP area is significantly increased in diabetes compared to control indicating an increase in excitability of the caps−lpH+ neurons including probability of their bursting in diabetic conditions. Numbers of cells: control for diabetes n = 20 from four rats, diabetes n = 28 from four rats, p < 0.05. d A representative trace of AP bursts generated in 25 % of diabetic neurons (n = 28 from four rats) at a threshold current stimulation. At the same time no AP bursts were observed in the caps−lpH+ neurons of control rats (n = 20 from four rats). e Application of amiloride converts ADPs (top left) and bursts (bottom left) observed in the diabetic caps−lpH+ neurons to AHPs (top and bottom right). f Diabetes leads to a statistically significant decrease in the AP threshold. Numbers of cells: control for diabetes n = 20 from four rats, diabetes n = 28 from four rats, p < 0.05
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4490764&req=5

Fig6: Diabetic-induced changes of the AP parameters for the caps−lpH+ neurons reflect increased excitability of these neurons in diabetes. a A representative AP trace with a slight AHP recorded from the caps−lpH+ neuron of normal rat. b A representative AP trace with a substantial ADP recorded from the caps−lpH+ neuron of diabetic rat. c The ADP/AHP area is significantly increased in diabetes compared to control indicating an increase in excitability of the caps−lpH+ neurons including probability of their bursting in diabetic conditions. Numbers of cells: control for diabetes n = 20 from four rats, diabetes n = 28 from four rats, p < 0.05. d A representative trace of AP bursts generated in 25 % of diabetic neurons (n = 28 from four rats) at a threshold current stimulation. At the same time no AP bursts were observed in the caps−lpH+ neurons of control rats (n = 20 from four rats). e Application of amiloride converts ADPs (top left) and bursts (bottom left) observed in the diabetic caps−lpH+ neurons to AHPs (top and bottom right). f Diabetes leads to a statistically significant decrease in the AP threshold. Numbers of cells: control for diabetes n = 20 from four rats, diabetes n = 28 from four rats, p < 0.05
Mentions: Correlation between the ADP/AHP area or the AP threshold and T-type current density was also directly established for the caps−lpH+ neurons (Fig 5) by measuring AP parameters and TCD for the same neuron in Tyrode’s and TEA-Cl, Ba2+-based solutions, respectively. Fig 6 clearly demonstrates a robust correlation between TCD and AP parameters characterizing neuronal excitability. Corresponding Pearson correlation coefficient and level of significance for correlation of the ADP/AHP area and the AP threshold with the TCD were 0.78, p < 1*E−5 and 0.7, p < 0.002, respectively. Thus, T-type current in the caps−lpH+ neurons is significantly correlated with the neuronal excitability parameters.Fig. 6

Bottom Line: This upregulation was not accompanied by significant changes in biophysical properties of T-type channels suggesting that a density of functionally active channels was increased.The upregulation of T-type channels resulted in the increased neuronal excitability of these nociceptive neurons revealed by a lower threshold for action potential initiation, prominent afterdepolarizing potentials and burst firing.Capsaicin-insensitive low-pH-sensitive type of DRG neurons shows diabetes-induced upregulation of Cav3.2 subtype of T-type channels.

View Article: PubMed Central - PubMed

Affiliation: Department of General Physiology of the CNS and State Key Laboratory of Molecular and Cellular Biology, Bogomoletz Institute of Physiology of National Academy of Science of Ukraine, 4 Bogomoletz street, 01024, Kyiv, Ukraine. dduzhyy@biph.kiev.ua.

ABSTRACT

Background: Previous studies have shown that increased excitability of capsaicin-sensitive DRG neurons and thermal hyperalgesia in rats with short-term (2-4 weeks) streptozotocin-induced diabetes is mediated by upregulation of T-type Ca(2+) current. In longer-term diabetes (after the 8th week) thermal hyperalgesia is changed to hypoalgesia that is accompanied by downregulation of T-type current in capsaicin-sensitive small-sized nociceptors. At the same time pain symptoms of diabetic neuropathy other than thermal persist in STZ-diabetic animals and patients during progression of diabetes into later stages suggesting that other types of DRG neurons may be sensitized and contribute to pain. In this study, we examined functional expression of T-type Ca(2+) channels in capsaicin-insensitive DRG neurons and excitability of these neurons in longer-term diabetic rats and in thermally hypoalgesic diabetic rats.

Results: Here we have demonstrated that in STZ-diabetes T-type current was upregulated in capsaicin-insensitive low-pH-sensitive small-sized nociceptive DRG neurons of longer-term diabetic rats and thermally hypoalgesic diabetic rats. This upregulation was not accompanied by significant changes in biophysical properties of T-type channels suggesting that a density of functionally active channels was increased. Sensitivity of T-type current to amiloride (1 mM) and low concentration of Ni(2+) (50 μM) implicates prevalence of Cav3.2 subtype of T-type channels in the capsaicin-insensitive low-pH-sensitive neurons of both naïve and diabetic rats. The upregulation of T-type channels resulted in the increased neuronal excitability of these nociceptive neurons revealed by a lower threshold for action potential initiation, prominent afterdepolarizing potentials and burst firing. Sodium current was not significantly changed in these neurons during long-term diabetes and could not contribute to the diabetes-induced increase of neuronal excitability.

Conclusions: Capsaicin-insensitive low-pH-sensitive type of DRG neurons shows diabetes-induced upregulation of Cav3.2 subtype of T-type channels. This upregulation results in the increased excitability of these neurons and may contribute to nonthermal nociception at a later-stage diabetes.

No MeSH data available.


Related in: MedlinePlus