Cutaneous blood flow. Laser Doppler velocimetry

The Biophysical Basis Underlying Gating Changes in the p.V1316A Mutant Nav1.7 Channel and the Molecular Pathogenesis of Inherited Erythromelalgia

The Na_v1.7 channel critically contributes to the excitability of sensory neurons, and gain-of-function mutations of this channel have been shown to cause inherited erythromelalgia (IEM) with neuropathic pain. In this study, we report a case of a severe phenotype of IEM caused by p.V1316A mutation in the Na_v1.7 channel. Mechanistically, we first demonstrate that the Na_vβ4 peptide acts as a gating modifier rather than an open channel blocker competing with the inactivating peptide to give rise to resurgent currents in the Na_v1.7 channel. Moreover, there are two distinct open and two corresponding fast inactivated states in the genesis of resurgent Na⁺ currents. One is responsible for the resurgent route and practically existent only in the presence of Na_vβ4 peptide, whereas the other is responsible for the “silent” route of recovery from inactivation. In this regard, the p.V1316A mutation makes hyperpolarization shift in the activation curve, and depolarization shift in the inactivation curve, vividly uncoupling inactivation from activation. In terms of molecular gating operation, the most important changes caused by the p.V1316A mutation are both acceleration of the transition from the inactivated states to the activated states and deceleration of the reverse transition, resulting in much larger sustained as well as resurgent Na⁺ currents. In summary, the genesis of the resurgent currents in the Na_v1.7 channel is ascribable to the transient existence of a distinct and novel open state promoted by the Na_vβ4 peptide. In addition, S4–5 linker in domain III where V1316 is located seems to play a critical role in activation–inactivation coupling, chiefly via direct modulation of the transitional kinetics between the open and the inactivated states. The sustained and resurgent Na⁺ currents may therefore be correlatively enhanced by specific mutations involving this linker and relevant regions, and thus marked hyperexcitability in corresponding neural tissues as well as IEM symptomatology.

Mutations in the Na_v1.7 sodium channel cause idiopathic erythromelalgia. This study shows that the pathogenic resurgent sodium currents arise via modification of gating behavior rather than via competing pore block by the Na_vβ4 peptide.

The gain-of-function mutation (p.V1316A) of the Na_v1.7 channel causes inherited erythromelalgia (IEM), a disease characterized by extremely enhanced activity in relevant neural tissues that results in neuropathic pain. We found that the p.V1316A mutation alters the basic gating properties of the channel, leading to increased sustained currents during membrane depolarization and resurgent currents during repolarization. Neurons expressing these mutant channels are more difficult to maintain in a hyperpolarized state and are thus more excitable. We demonstrate that there is very likely a distinct set of open/inactivated (O/I) states responsible for the genesis of resurgent currents. We show that the p.V1316A mutation chiefly accelerates the I to O transition in this set, but also decelerates the transitions between different sets of O/I states, to cause the channel gating and cellular excitability changes. Contrary to the conventional view, we find that the Na_vβ4 peptide, a key element responsible for sizable resurgent currents, does not seem to act as a pore blocker that competes with the inactivation peptide. Instead, we show that it acts as a gating modifier of the Na_v1.7 channel. Thus, the DIII/S4–5 linker, where V1316 is located, may play a critical role not only in O/I coupling but also in the couplings between different sets of O/I in the Na_v1.7 channel.

Arterial blood flow and microcirculatory changes in a rat groin flap after thrombosis induced by electrical stimulation of the artery

An experimental model of acute arterial thrombosis was developed in a rat groin flap model. Electrical stimulation was delivered to the flap artery while measuring blood flow in the artery and in the flap microcirculation using a laser Doppler system. Electrical stimulation produced an occlusive thrombosis in 10 rats within 68.1 +/- 19.26 (mean +/- SE) min. Thrombosis formation produced a rapid decrease of the LDF readings in the artery (90%) and in the flap (70%), the decrease being fairly parallel. Following the spontaneous thrombolysis, the artery perfusion recovered to baseline level but the flap blood flow only recovered by 10-20%. During electrical stimulation there was no change of the systemic blood pressure. The dynamic course of thrombus formation was documented on a videotape recorder through a microscope-mounted video camera and monitored on a television screen. Segments of the artery were obtained during and at the end of the experiments. The histological examination revealed arterial thrombosis composed of red blood cells, fibrin, and white blood cells, without any significant architectural and endothelial changes in the vessel walls. The study suggests that this model using electric vessel stimulation is effective for inducing arterial thrombosis and provides a simple method for recording the dynamic course of thrombus formation.

Cutaneous blood flow and adrenoceptor response increase in segmental-type vitiligo lesions

It has been proposed that two types of vitiligo exist from the physiological and clinical points of view. Nonsegmental-type vitiligo is associated with autoimmune diseases while segmental-type vitiligo results from the dysfunction of sympathetic nerves in the affected area. Using laser Doppler flowmetry and iontophoresis for cutaneous microcirculatory assessments, we evaluated these two types of vitiligo in regard to their physiological changes. Ten patients with facial stable stage segmental-type vitiligo and ten stable nonsegmental-type vitiligo patients were selected for this study. Our results revealed that a nearly threefold increase in cutaneous blood flow was noticed in segmental-type vitiligo as compared to contralateral normal skin. In contrast, a 1.4-1.5 times difference was found among nonsegmental-type vitiligo, lesion side clinically normal skin and contralateral normal skin. There was a significant increase in cutaneous alpha- and beta-adrenoceptor response in segmental-type vitiligo lesions. However, no change in plasma catecholamines or adrenoceptor densities on blood cells was noticed. Our findings suggest that a dysfunction of the sympathetic nerves exists in the affected skin and plays a role in the pathogenesis of segmental-type vitiligo.

Increased cutaneous blood flow but impaired post-ischemic response of nutritional flow in obese children

It is well known that cardiovascular risk factors and dyslipidemia along with obesity can be identified early in life. Serum lipids and lipoproteins influence skin vessel reactivity in adults. The purpose of this study was to investigate the cutaneous microcirculation and its correlation to dyslipidemia in obese children. Thirty-four obese children and an equal number of age- and sex-matched healthy children were enrolled in this study. Laser Doppler flowmetry and dynamic capillaroscopy were performed to measure total cutaneous blood flow and nutritional blood flow, respectively. A significantly higher cutaneous baseline flow and peak flow after a 1-min arterial occlusion was noticed in obese group as compared to normal control. Results of dynamic capillaroscopy revealed values of resting capillary blood cell velocity that did not differ from controls but a significantly lower peak CBV after a 1-min arterial occlusion in obesity. Plasma lipids examination showed a high triglycerides and low high density lipoprotein cholesterol levels in obesity. Pearson analysis detected no significant correlations between pCBV, baseline flow and peak flow and dyslipidemia in obesity. These results may be explained by the fact that the duration of dyslipidemia in our study population was not long enough to cause vascular damage or the dyslipidemia was not pronounced enough to have an impact on skin vessel activity tests. It is also possible, that the combination of methods used in the present study was not sensitive enough to detect an existing correlations between flow values and high triglycerides/low HDL-cholesterol values in the obese group. Our results suggest that all the responses of the cutaneous microcirculation were mainly due to physiological compensatory rather than pathological reactions in young obese children. The results of cutaneous microcirculatory assessment in obese children provide follow-up parameters for assessing the risk of cardiovascular diseases later in life.

Topical hydrogen peroxide treatment of ischemic ulcers in the guinea pig: blood recruitment in multiple skin sites

BACKGROUND

Oxygen deficit is a key factor associated with delayed healing of ischemic wounds in human beings. Topical oxygen-releasing compounds such as hydrogen peroxide or tetrachlorodecaoxide have been suggested as therapy for ischemic tissue.

OBJECTIVE

Our purpose was to monitor the effect of hydrogen peroxide cream on the process of ischemic ulcer healing with a model for ischemic ulcers in the guinea pig.

METHODS

Measurement of vascular perfusion with a laser Doppler velocimeter and gross observations of percentage of nonnecrotic wound surface were made on ischemic wounds in guinea pigs after treatment with either a hydrogen peroxide cream or a placebo cream.

RESULTS

Visual evaluations of the percentage of nonnecrotic wound surface showed no statistically significant differences among the treatments. In contrast, vascular perfusion measurements resulted in statistically significant differences. Blood flow was significantly higher up to day 15 in ulcers treated with 2% hydrogen peroxide cream than in those treated with placebo cream. Vascular perfusion was significantly higher in ulcers treated with 3.5% hydrogen peroxide cream than in ulcers treated with either 1.5% hydrogen peroxide cream or placebo. Adjacent control sites in guinea pigs whose ulcers were treated with hydrogen peroxide cream showed increased vascular perfusion compared with corresponding sites in animals whose ulcers were treated with placebo. Even distant flank control sites of ulcers treated with 3.5% hydrogen peroxide cream showed increased vascular perfusion.

CONCLUSION

Treatment of ischemia-induced ulcers with hydrogen peroxide cream enhanced cutaneous blood recruitment not only to ulcers and adjacent sites, but also to distant sites.

Cutaneous blood flow abnormalities in hypertriglyceridemia

An accelerated atherosclerosis, in particular of the coronary arteries, was documented in hypertriglyceridemia. The objective of the present study was to assess the cutaneous dynamic blood flow in hypertriglyceridemia, utilizing the optical noninvasive method of laser Doppler flowmetry. The cutaneous blood flow on the forearms was measured during the postischemic reactive hyperemia test in treated and non-treated patients with hypertriglyceridemia and healthy control subjects. The subjects were 32 patients with hypertriglyceridemia--15 untreated and 17 following 6-9 months of bezafibrate treatment--and 27 healthy control subjects. In untreated patients with hypertriglyceridemia, the peak flow was significantly lower than in both the treated group (p < 0.005) and control group (p < 0.02). Similarly, the area under the response-time curve of the untreated patients with hypertriglyceridemia was smaller (p < 0.01 and p < 0.05, respectively). These parameters were similar in the treated group and the control group. The reaction was faster in the treated group, as compared to the other two groups (p < 0.001). The control group exhibited a longer time to decay than the treated group (p < 0.01). Postischemic reactive hyperemia tests in patients with hypertriglyceridemia reveal cutaneous microcirculatory changes in the forearm. These changes may arise from several mechanisms, including functional abnormalities of the endothelium or vascular smooth muscle, or structural changes in the blood vessels that limit vasodilatation. These changes are reversible, and corrected when reducing the triglyceride levels, but other abnormalities are then present, suggesting a permanent damage. These dynamic measurements of cutaneous blood flow are sensitive indicators of atherogenesis, and can be employed for the evaluation of microvascular involvement and follow-up of patients with hypertriglyceridemia.

Dermal vascularity in lentigo maligna

Lentigo maligna (LM) may represent a tumour arrested in an in situ phase, lacking the angiogenic capacity and underlying dermal neovascularization required for invasive growth. The acquisition of an angiogenic phenotype might be associated with the development of lentigo maligna melanoma (LMM). To investigate this thesis, sections of formalin-fixed, paraffin-embedded tissue from 15 LMMs, and 11 LM excision specimens were stained with the vascular endothelial marker Ulex europaeus agglutinin I. Dermal vessels were counted and vascular morphometry was performed. In specimens in which LMM was present, dermal vascularity was significantly increased in LM compared with normal skin. The most significant increases were found for dermal vascular density (39 per cent increase, P = 0.008) and for total vessel surface area (62 per cent increase, P = 0.005). However, when no LMM was present, the vascular density underlying LM (79 +/- 9 vessels/mm2) did not differ significantly from that of adjacent normal skin (67 +/- 6 vessels/mm2), although focal 'hot spots' of increased vascularity were present. We conclude that increased dermal vascularity is present beneath in situ LM and that this increased vascular density is closely associated with the presence of invasive LMM in the same specimen.

Cutaneous blood flow in gestational hypertension and normal pregnancy

A laser Doppler flowmeter was used to assess skin blood flow changes in three groups of young subjects: women with gestational hypertension, healthy pregnant women, and healthy non-pregnant women. Responses to four vasoactive stimuli were studied: isometric and cognitive activities, cutaneous post ischemic reactive hyperemia, and local heating. The first two stimuli are vasoconstrictive and were performed on the fingertip, whereas the latter two are vasodilative and were performed on the forearm. The most prominent differences were observed in the isometric test, where the expected decrease, which was indeed registered in non-pregnant women, was almost absent in the healthy pregnant group. The gestational hypertension group had a greater decrease in blood flow than normal pregnancy, but lesser than non-pregnant control subjects. We conclude that although normal pregnancy modifies the response of the skin microvasculature to some vasoactive stimuli, gestational hypertension pushes that response back toward the non-pregnancy state.