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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

Diabetes-induced upregulation of T-type channels in the caps−lpH+ neurons of hypoalgesic subgroup of diabetic rats. a Representative traces of Ba2+ current in the caps−lpH+ neurons isolated from the control (upper traces), hypoalgesic (lower traces) diabetic rats. b Significant increase of TCD was observed in the caps−lpH+ neurons of diabetic compared to control rats in a range of −60 - -0 mV where Ba2+ current is mediated by T-type channels (n = 8 and n = 7, from three animals each, for control and diabetic groups, respectively; *p < 0.05). The caps−lpH+ neurons were isolated from diabetic animals after 6 weeks of STZ-induced diabetes. The currents were evoked by depolarizing steps from a holding potential of −100 mV to −80 through 0 mV in 10 mV increments. An insert demonstrates TCD amplitude for each tested neuron and their mean values (boxes C - for the control and D - for the diabetes) with standard errors (upper whiskers) at a depolarization step to −50 mV
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Fig3: Diabetes-induced upregulation of T-type channels in the caps−lpH+ neurons of hypoalgesic subgroup of diabetic rats. a Representative traces of Ba2+ current in the caps−lpH+ neurons isolated from the control (upper traces), hypoalgesic (lower traces) diabetic rats. b Significant increase of TCD was observed in the caps−lpH+ neurons of diabetic compared to control rats in a range of −60 - -0 mV where Ba2+ current is mediated by T-type channels (n = 8 and n = 7, from three animals each, for control and diabetic groups, respectively; *p < 0.05). The caps−lpH+ neurons were isolated from diabetic animals after 6 weeks of STZ-induced diabetes. The currents were evoked by depolarizing steps from a holding potential of −100 mV to −80 through 0 mV in 10 mV increments. An insert demonstrates TCD amplitude for each tested neuron and their mean values (boxes C - for the control and D - for the diabetes) with standard errors (upper whiskers) at a depolarization step to −50 mV

Mentions: Subgroups of hypoalgesic and hyperalgesic rats were isolated within a group of 6–7 week STZ-diabetic animals by measuring time of hind paw withdrawal latency, PWL, under thermal stimulation. A diabetic rat was considered to be hypo- or hyperalgesic if its PWL was correspondently higher or lower than the 95 % confidence interval for PWL distribution of the control group, which was 16.6÷19.4 s. Hypoalgesic and hyperalgesic subgroups had correspondently significantly higher (28.3 ± 1.4 s, 32 tests from three rats) or lower (11.8 ± 0.8 s, 19 tests from three rats) averaged PWL compared to control (18 ± 0.7 sec, 28 tests from three rats; p < 0.001). Blood glucose level in animals of both diabetic subgroups was significantly higher than in control animals, while mean body weights for both subgroups were not significantly different from control at 6–7 weeks of diabetes (Table 1). These results are similar to ones obtained in the previous work [10], in which downregulation of T-type current was shown in caps+ nociceptive neurons. Representative families of total Ba2+ currents in the caps−lpH+ neurons from control and hypoalgesic animals are shown in Fig 3a. It has appeared that the caps−lpH+ neurons showed upregulation of low voltage-activated Ba2+ current in diabetic hypoalgesic animals (Fig 3). The averaged current–voltage curves of a transient component normalized to a cell capacitance are shown in Fig 3b. An increase in TCD in the caps−lpH+ neurons isolated from hypoalgesic rats was significant and varied from 2.6-fold at a voltage step to −60 mV to 2.8-fold at a voltage step to −40 mV (Fig 3b). Observed upregulation of T-type current in the caps−lpH+ neurons of 6–7 weeks diabetic hypoalgesic rats was opposite to previously found downregulation of T-type current in the caps+ nociceptors of the same animal group [10]. Thus, this upregulation was due to specific sensory modalities of the caps−lpH+ neurons rather than due to differences in the age of animals or duration of diabetes. It also suggests involvement of TRPV1-independent signal transduction pathway in upregulation of T-type current in the caps−lpH+ DRG neurons under diabetic conditions. Upregulation of T-type current in the caps−lpH+ neurons of thermally hypoalgesic diabetic rats implies their involvement in nonthermal nociception.Fig. 3


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)

Diabetes-induced upregulation of T-type channels in the caps−lpH+ neurons of hypoalgesic subgroup of diabetic rats. a Representative traces of Ba2+ current in the caps−lpH+ neurons isolated from the control (upper traces), hypoalgesic (lower traces) diabetic rats. b Significant increase of TCD was observed in the caps−lpH+ neurons of diabetic compared to control rats in a range of −60 - -0 mV where Ba2+ current is mediated by T-type channels (n = 8 and n = 7, from three animals each, for control and diabetic groups, respectively; *p < 0.05). The caps−lpH+ neurons were isolated from diabetic animals after 6 weeks of STZ-induced diabetes. The currents were evoked by depolarizing steps from a holding potential of −100 mV to −80 through 0 mV in 10 mV increments. An insert demonstrates TCD amplitude for each tested neuron and their mean values (boxes C - for the control and D - for the diabetes) with standard errors (upper whiskers) at a depolarization step to −50 mV
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig3: Diabetes-induced upregulation of T-type channels in the caps−lpH+ neurons of hypoalgesic subgroup of diabetic rats. a Representative traces of Ba2+ current in the caps−lpH+ neurons isolated from the control (upper traces), hypoalgesic (lower traces) diabetic rats. b Significant increase of TCD was observed in the caps−lpH+ neurons of diabetic compared to control rats in a range of −60 - -0 mV where Ba2+ current is mediated by T-type channels (n = 8 and n = 7, from three animals each, for control and diabetic groups, respectively; *p < 0.05). The caps−lpH+ neurons were isolated from diabetic animals after 6 weeks of STZ-induced diabetes. The currents were evoked by depolarizing steps from a holding potential of −100 mV to −80 through 0 mV in 10 mV increments. An insert demonstrates TCD amplitude for each tested neuron and their mean values (boxes C - for the control and D - for the diabetes) with standard errors (upper whiskers) at a depolarization step to −50 mV
Mentions: Subgroups of hypoalgesic and hyperalgesic rats were isolated within a group of 6–7 week STZ-diabetic animals by measuring time of hind paw withdrawal latency, PWL, under thermal stimulation. A diabetic rat was considered to be hypo- or hyperalgesic if its PWL was correspondently higher or lower than the 95 % confidence interval for PWL distribution of the control group, which was 16.6÷19.4 s. Hypoalgesic and hyperalgesic subgroups had correspondently significantly higher (28.3 ± 1.4 s, 32 tests from three rats) or lower (11.8 ± 0.8 s, 19 tests from three rats) averaged PWL compared to control (18 ± 0.7 sec, 28 tests from three rats; p < 0.001). Blood glucose level in animals of both diabetic subgroups was significantly higher than in control animals, while mean body weights for both subgroups were not significantly different from control at 6–7 weeks of diabetes (Table 1). These results are similar to ones obtained in the previous work [10], in which downregulation of T-type current was shown in caps+ nociceptive neurons. Representative families of total Ba2+ currents in the caps−lpH+ neurons from control and hypoalgesic animals are shown in Fig 3a. It has appeared that the caps−lpH+ neurons showed upregulation of low voltage-activated Ba2+ current in diabetic hypoalgesic animals (Fig 3). The averaged current–voltage curves of a transient component normalized to a cell capacitance are shown in Fig 3b. An increase in TCD in the caps−lpH+ neurons isolated from hypoalgesic rats was significant and varied from 2.6-fold at a voltage step to −60 mV to 2.8-fold at a voltage step to −40 mV (Fig 3b). Observed upregulation of T-type current in the caps−lpH+ neurons of 6–7 weeks diabetic hypoalgesic rats was opposite to previously found downregulation of T-type current in the caps+ nociceptors of the same animal group [10]. Thus, this upregulation was due to specific sensory modalities of the caps−lpH+ neurons rather than due to differences in the age of animals or duration of diabetes. It also suggests involvement of TRPV1-independent signal transduction pathway in upregulation of T-type current in the caps−lpH+ DRG neurons under diabetic conditions. Upregulation of T-type current in the caps−lpH+ neurons of thermally hypoalgesic diabetic rats implies their involvement in nonthermal nociception.Fig. 3

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