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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

Excitability of the caps−lpH+ neurons is decreased under T-type channel blockers. T-type channel blockers convert the ADP to AHP and significantly increase the AP threshold for the caps−lpH+ neurons at concentrations effectively blocking the Cav3.2 isoform of T-type channels. a,b Action potential parameters used for estimation of changes in excitability of the caps−lpH+ DRG neurons (action potential threshold (APT) and after-depolarization/-hyperpolarization areas (ADP/AHP)). c An example of an AP burst induced by a threshold stimulation in the caps−lpH+ neuron of longer-term diabetic rat instead of a single AP observed in the neurons of normal rats. d Significant decrease of the Ba2+ TCD in the caps−lpH+ neurons under T-type channel blockers Ni2+ (50 μM) and amiloride (1 mM). TCD amplitudes at a voltage step from −100 to −50 mV are presented. Insert: representative traces of Ba2+ current before and after application of 50 μM Ni2+. e A representative example of the AP parameter changes in the caps−lpH+ neurons of diabetic rats under T-type channel blocker, Ni2+ (50 μM). The ADP converted to AHP and the AP threshold increased in 50 μM Ni2+ (grey trace) compared to control (black trace). The ADP and AHP areas are cross-hatched. The AP threshold levels are indicated by dashed lines. f,h The ADP/AHP area reversed from positive to negative values under 50 μM Ni2+ (f) and 1 mM amiloride (h) reflecting conversion of the ADP to AHP shown on (e). g,i Significant AP threshold increase under 50 μM Ni2+ (g) and 1 mM amiloride (i) Numbers of cells: Ni2+ inhibition, n = 6 from three rats; amiloride inhibition, n = 6 from three rats. *p < 0.05, **p < 0.01
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Fig4: Excitability of the caps−lpH+ neurons is decreased under T-type channel blockers. T-type channel blockers convert the ADP to AHP and significantly increase the AP threshold for the caps−lpH+ neurons at concentrations effectively blocking the Cav3.2 isoform of T-type channels. a,b Action potential parameters used for estimation of changes in excitability of the caps−lpH+ DRG neurons (action potential threshold (APT) and after-depolarization/-hyperpolarization areas (ADP/AHP)). c An example of an AP burst induced by a threshold stimulation in the caps−lpH+ neuron of longer-term diabetic rat instead of a single AP observed in the neurons of normal rats. d Significant decrease of the Ba2+ TCD in the caps−lpH+ neurons under T-type channel blockers Ni2+ (50 μM) and amiloride (1 mM). TCD amplitudes at a voltage step from −100 to −50 mV are presented. Insert: representative traces of Ba2+ current before and after application of 50 μM Ni2+. e A representative example of the AP parameter changes in the caps−lpH+ neurons of diabetic rats under T-type channel blocker, Ni2+ (50 μM). The ADP converted to AHP and the AP threshold increased in 50 μM Ni2+ (grey trace) compared to control (black trace). The ADP and AHP areas are cross-hatched. The AP threshold levels are indicated by dashed lines. f,h The ADP/AHP area reversed from positive to negative values under 50 μM Ni2+ (f) and 1 mM amiloride (h) reflecting conversion of the ADP to AHP shown on (e). g,i Significant AP threshold increase under 50 μM Ni2+ (g) and 1 mM amiloride (i) Numbers of cells: Ni2+ inhibition, n = 6 from three rats; amiloride inhibition, n = 6 from three rats. *p < 0.05, **p < 0.01

Mentions: Next, we studied whether upregulation of T-type current observed in the caps−lpH+ neurons of longer-term diabetic rats resulted in increased excitability of these neurons. Excitability was estimated based on two parameters of neuronal APs: the action potential threshold (APT) determined at a threshold current stimulation evoking an AP (Fig 4a) and the afterhyperpolarization/afterdepolarization (AHP/ADP) area (Fig 4a,b). A fitted part of a trace used to estimate an APT and AHP/ADP area are shown in grey on the Fig 4a,b. An increase in the ADP area as well as a decrease in the APT were considered to be indications of increased neuronal excitability since the former may cause burst firing (Fig 4c, [5]) and the latter should lower sensory input necessary to induce AP.Fig. 4


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)

Excitability of the caps−lpH+ neurons is decreased under T-type channel blockers. T-type channel blockers convert the ADP to AHP and significantly increase the AP threshold for the caps−lpH+ neurons at concentrations effectively blocking the Cav3.2 isoform of T-type channels. a,b Action potential parameters used for estimation of changes in excitability of the caps−lpH+ DRG neurons (action potential threshold (APT) and after-depolarization/-hyperpolarization areas (ADP/AHP)). c An example of an AP burst induced by a threshold stimulation in the caps−lpH+ neuron of longer-term diabetic rat instead of a single AP observed in the neurons of normal rats. d Significant decrease of the Ba2+ TCD in the caps−lpH+ neurons under T-type channel blockers Ni2+ (50 μM) and amiloride (1 mM). TCD amplitudes at a voltage step from −100 to −50 mV are presented. Insert: representative traces of Ba2+ current before and after application of 50 μM Ni2+. e A representative example of the AP parameter changes in the caps−lpH+ neurons of diabetic rats under T-type channel blocker, Ni2+ (50 μM). The ADP converted to AHP and the AP threshold increased in 50 μM Ni2+ (grey trace) compared to control (black trace). The ADP and AHP areas are cross-hatched. The AP threshold levels are indicated by dashed lines. f,h The ADP/AHP area reversed from positive to negative values under 50 μM Ni2+ (f) and 1 mM amiloride (h) reflecting conversion of the ADP to AHP shown on (e). g,i Significant AP threshold increase under 50 μM Ni2+ (g) and 1 mM amiloride (i) Numbers of cells: Ni2+ inhibition, n = 6 from three rats; amiloride inhibition, n = 6 from three rats. *p < 0.05, **p < 0.01
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4490764&req=5

Fig4: Excitability of the caps−lpH+ neurons is decreased under T-type channel blockers. T-type channel blockers convert the ADP to AHP and significantly increase the AP threshold for the caps−lpH+ neurons at concentrations effectively blocking the Cav3.2 isoform of T-type channels. a,b Action potential parameters used for estimation of changes in excitability of the caps−lpH+ DRG neurons (action potential threshold (APT) and after-depolarization/-hyperpolarization areas (ADP/AHP)). c An example of an AP burst induced by a threshold stimulation in the caps−lpH+ neuron of longer-term diabetic rat instead of a single AP observed in the neurons of normal rats. d Significant decrease of the Ba2+ TCD in the caps−lpH+ neurons under T-type channel blockers Ni2+ (50 μM) and amiloride (1 mM). TCD amplitudes at a voltage step from −100 to −50 mV are presented. Insert: representative traces of Ba2+ current before and after application of 50 μM Ni2+. e A representative example of the AP parameter changes in the caps−lpH+ neurons of diabetic rats under T-type channel blocker, Ni2+ (50 μM). The ADP converted to AHP and the AP threshold increased in 50 μM Ni2+ (grey trace) compared to control (black trace). The ADP and AHP areas are cross-hatched. The AP threshold levels are indicated by dashed lines. f,h The ADP/AHP area reversed from positive to negative values under 50 μM Ni2+ (f) and 1 mM amiloride (h) reflecting conversion of the ADP to AHP shown on (e). g,i Significant AP threshold increase under 50 μM Ni2+ (g) and 1 mM amiloride (i) Numbers of cells: Ni2+ inhibition, n = 6 from three rats; amiloride inhibition, n = 6 from three rats. *p < 0.05, **p < 0.01
Mentions: Next, we studied whether upregulation of T-type current observed in the caps−lpH+ neurons of longer-term diabetic rats resulted in increased excitability of these neurons. Excitability was estimated based on two parameters of neuronal APs: the action potential threshold (APT) determined at a threshold current stimulation evoking an AP (Fig 4a) and the afterhyperpolarization/afterdepolarization (AHP/ADP) area (Fig 4a,b). A fitted part of a trace used to estimate an APT and AHP/ADP area are shown in grey on the Fig 4a,b. An increase in the ADP area as well as a decrease in the APT were considered to be indications of increased neuronal excitability since the former may cause burst firing (Fig 4c, [5]) and the latter should lower sensory input necessary to induce AP.Fig. 4

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