Electric field stimulation

Summation The overall response is the arithmetic sum of the contribution brought by each receptor (e.g., NKX and NK2). Capsaicin-induced contraction of rat isolated urinary bladder, electrical field stimulation (EFS)-induced nonadrenergic, noncholinergic contraction of the isolated guinea pig bronchus or renal pelvis when SP metabolism is blocked by peptidase inhibitors are all examples of summation. Both NK and NK2r antagonists are required to abolish such kind of response, but each antagonist substantially reduces the response... 

EDTA Ethylenediamine tetraacetic acid ako known as etidronic acid EE Eosinophilic eosinophils EEG Electroencephalogram EET Epoxyeicosatrienoic acid EFA Essential fatty acid EFS Electrical field stimulation EGl Monoclonal antibody specific for the cleaved form of eosinophil cationic peptide... 

Increased extracellular ATP breakdown has been seen in vitro during electrical field stimulation and during hypoxia (Lloyd et al., 1993). Although this source of extracellular adenosine accumulation remains a possibility, it has been found that inhibition of extracellular AMP hydrolysis does not significantly affect adenosine levels (Rosenberg et al., 2000). The main source of adenosine is thus probably intracellular, and possibly related to increased energy consumption. 

Phillips, T.E., Phillips, T.H. and Neutra, M.H. (1984) Regulation of intestinal goblet cell secretion. IV. Electrical field stimulation in vitro. American Journal of Physiology 247, G682—G687. 

Ignarro, L. I, Bush, P. A., Buga, G. M., Wood, K. S., Fukuto, J. M., and Rajfer, J., 1990, Nitric oxide and cychc GMP formation upon electrical field stimulation cause relaxation of corpus cavemosum smooth muscle, Biochem. Biophys. Res. Commun. 170 843-850. 

As far as man is concerned, a presynaptic inhibition of the noradrenaline release by H3 receptors was only studied in the isolated human saphenous vein In this tissue, these receptors, similarly to a2-adrenoceptors, decrease the 3H-noradrenaline overflow elicited by electrical field stimulation (Molderings et al., 1992). Therefore, the role of histamine H3-receptors in the global control of the blood pressure in humans cannot be stated at present. 

In contrast, noradrenergic sympathetic innervation of the airways is sparse, and these fibers do not appear to play a major role in controlling airway diameter. Bronchodilation may be brought about by nonadrenergic, noncholinergic nerves releasing nitric oxide since nitric oxide synthase inhibitors have been shown to reduce bronchodilation produced by electrical field stimulation in vitro. 

The electric field-stimulated uptake of macromolecules is temperature dependent whereas stimulated adsorption is not. For example, the uptake of BSA-FITC by COS 5-7 cells is almost completely diminished at 4°C and enhanced twofold at 37°C compared with room temperature. When elevating the temperature during exposure, one should take into account that LEF treatment also leads to temperature elevation in the cell suspension. The temperature of the solutions during exposure can be measured using fiber-optic temperature sensors (FISO Technologies, Quebec, Canada). Transient temperature rise by up to 2°C can be measured at the end of 1 min exposure of DMEM-H medium to LEF (20 V/cm, 180 (jls pulse duration, and 500 Hz frequency). 

Color Plate 2 Low electric field-stimulated adsorption and uptake of... 

Bumstock et al. (1978) used recorded isometric tension of mucosal-free strips of the detrusor of the bladder from guinea pigs in vitro after electrical field stimulation. 

Electrical field stimulation is applied to either compartment by means of two wire platinum electrodes positioned in parallel with the two sides of the ureter. Square wave pulses (5-25 ms pulse width, 20 V) are automatically delivered every 100 s by means of a GRASS S88 stimulator. 

A phosphoramidon-sensitive ECE has been identified by functional studies in rat vas deferens [170] and therefore this is a potential isolated tissue screen for testing ECE inhibitors. Big ET-1, 3-600 nM, increases the twitch height to electrical field stimulation in the isolated vas deferens preparation and this effect is inhibited in the presence of phosphoramidon... 

The activation of NOS or the products thereof modulates airway constrictor responses as well. Atropine-sensitive, electrical field stimulation-induced bronchoconstrictor responses in the guinea-pig are enhanced by NOS inhibitors (Belvisi etal., 1991). Nitrogen oxides also modulate the effects of non-cholinergic bronchoconstrictors. H stimulation of Hi receptors in the guinea-pig lung leads... 

Ellis, J.L. and Undem, B.J. (1992). Antigen-induced enhancement of noncholinergic contractile responses to v us nerve and electrical field stimulation in guinea-pig isolated trachea. J. Pharmacol. Exp. Ther. 262, 646-653. 

Farmer, S.G. and Togo, J. (1990). Eflfects of epithelium removal on relaxation of airway smooth muscle induced by vasoactive intestinal peptide and electrical field stimulation. Br. J. Pharmacol. 100, 73-78. 

As opposed to the two other endogenous excitatory amino acid candidates, cystelc acid and cysteine sulphinlc acid (15), glutamate (16) and aspartate (13) are found in abundant quantities in the mammalian CNS. Metabolically, aspartate and glutamate are related and their metabolism is quite complex. Thus, there are undoubtedly several metabolic pools of glutamate and aspartate, in addition to any neurotransmitter pool, making it difficult to study the biochemical aspects of their neurotransmitter action. Nevertheless, it has been shown that both substances are accumulated into brain tissue by a high affinity process, and that both can be released from brain tissue by electrical field stimulation. This behavior is characteristic of neurotransmitters. 

Relaxant responses to electrical field stimulation (0.5 - 16 Hz) in guinea-pig taenia coli were inhibited by PPADS at the same concentration-range as were the responses to exogenous ATP and 2-methylthio ATP (Figure 4) [31], In the presence of 100 pM PPADS, these neurogenic relaxations were (compared to controls) 10% (0.5 Hz), 6% (2 Hz), 5% (8 Hz) and 4% (16 Hz). This supports the purinergic nerve hypothesis, which postulates ATP or a related compound as NANC-transmitter [2]. 

Paton and Zar (1968) described the dissection of the MP-LMP of the guinea-pig small intestine. This preparation has been invaluable in the study of neurotransmission from the myenteric plexus to the longitudinal smooth muscle, particularly by opioids and cannabinoids, without the confounding effects of the peristaltic reflex. A similar preparation has been used to study neuromuscular transmission to the circular smooth muscle (Izzo et al. 1998). Contractions of MP-LMP induced by electrical field stimulation (EES) were potently inhibited in a concentration-dependent fashion by the cannabinoid receptor agonists CP 55,940, CP 50,556, WIN 55,212-2, nabilone, CP 56,667, A -THC and cannabinol (Coutts and Pertwee 1997 Pertwee 2001). This inhibition was competitively and reversibly antagonised by SR141716A, without any effect on the inhibitory responses to normorphine... 

Figure 1 Contractions evoked in guinea-pig vena cava by electrical field stimulation at 40 Hz for 10 s (arrows), shown before and after pretreatment with SR 120107A (1 (x.Vl) (top panel) or BIBP 3226 (1 p,M) (lower panel). Note that it is mainly the prolonged contraction that is reduced in the presence of the Y1-receptor antagonists.

Figure 5 Inhibitory effect of SR 120819A on the electrically stimulated rabbit vas deferens. Cumulative concentration-response curves for [Leu31,Pro34]NPY on the amplitude of twitch contractions elicited by electrical field stimulation were established in the absence ( ) or in the presence of 0.1 (A), 0.3 ( ) and 1 (T) p.M of SR 120819A. Results are expressed as a percentage of the twitch control responses measured after 45 min incubation with or without SR 120819A, and are the mean SEM of 5-6 experiments.

At, 4 °C, no ATP-dependent Na+, K+, or Rb+ pumping activities sensitive to ouabain were detected. An ac electric field stimulated active efflux of Na+ and influx of K+ and Rb+ but not the passive influx of Na+ and efflux of K+ and Rb+. This ac-stimulated active transport of cations was completely inhibited by 0.2 mM of ouabain. At 26 °C, the enzyme hydrolyzed ATP to pump Na+ and K+. An ac stimulation further increased the rate of pumping. At 37 °C, the ATP hydrolysis of the enzyme was at its maximum and an ac stimulation did not escalate the rate of active pumping of these ions. 

Figure 1. Amplitude dependence of electric-field stimulated Na + pumping (A) and Rb + pumping (B). Na+ efflux was measured with the ac field at 1 MHz and Rb + influx was measured at 1 kHz. 1 MHz and 1 kHz are the optimal frequencies of the Na+ pump and the Rb+ pump, respectively. Key , sample not stimulated with ac field , sample stimulated with ac field , sample not stimulated with ac field, in the presence of 0.2-mM ouabain O, sample stimulated with ac field, in the presence of 0.2-mM ouabain. 1 amole / RBC-hr = 0.0108 mmol/ L of cells per hour, where RBC is red blood cell count. These measurements were done at 3 °C. (Adapted from reference 30.)...

Figure 2. Frequency dependence of electric-field-stimulated Na + pumping (A) and Rb + pumping (B). Afield strength of 20 V/cm (peak-to-peak) was used in both cases. Symbols are the same as in Figure 1. These measurements were done at 3 °C. (Adapted from reference 30.)...

Figure 3. Frequency dependence of electric-field-stimulated ATP hydrolysis activity of a highly purified Ecto nucleotide diphosphohydrolase. The ATP splitting activity of the detergent-solubilized Ecto enzyme was measured at 37 °C in the absence of acfield (a,), in the presence of 5.0-V/cm (peak-to-peak) ac field (O), and in the presence of 10-mM vanadate (a). Buffer 0.1% of detergent NP40, 30-mM histidine, 4-mM ATP, 4-rnM Mg2+, at pH 7.4. The optimal amplitude of stimulation is 5.0 V/cm with a 10-kHz ac field. (Adapted from...

The kinetics of contraction have been evaluated in electrically stimulated smooth muscle because under these conditions activation is not diffusion limited (Kamm and Stull 1985). Maximal values of unloaded shortening velocity and LC20 phosphorylation were attained after 5 s of stimulation and preceded maximd force. In a similar manner, maximal phosphorylation values were obtained after 3 to 4 s of electrical field stimulation of chicken gizzard strips while force was maximal after 5.5 s (Fischer and Pfitzer 1989). There is about a 500 ms lag time following stimulation and onset of LC20 phosphorylation in the electrically stimu-... 

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