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At least 1,549 records · Page 86Linked to original sources
PubMed1992

A voltage-clamp analysis of NMDA-induced responses on dopaminergic neurons of the rat substantia nigra zona compacta and ventral tegmental area.

The effects of NMDA-receptor activation on dopaminergic neurons of the rat substantia nigra zona compacta and ventral tegmental area were studied by using in vitro intracellular electrophysiological recordings (current and voltage-clamp). NMDA depolarized the membrane and increased the firing activity. A voltage-dependent inward current and a reduction of the apparent input conductance were observed in voltage-clamp experiments. Interestingly, the peak amplitude of the inward current occurred at approximately -60 mV. The NMDA-induced responses were reduced by the application of DL-2-amino-5-phosphonovaleric acid (APV). The NMDA-induced current was unaffected by potassium channel blockers, was present in low-sodium solutions or in solutions treated with TTX; but was reduced or blocked in low-calcium solutions containing cobalt. In addition, no reduction of the apparent input conductance was observed either in the solutions without magnesium or in those with low-sodium. Our data indicate that the activation of NMDA receptors produces a powerful excitatory stimulus on the dopaminergic neurons of the ventral mesencephalon and this may be primarily the result of a voltage-dependent influx of calcium ions. The degeneration of the dopaminergic cells after application of neurotoxins may be explained by their peculiar response to NMDA.

2-Amino-5-phosphonovalerate↗
PubMed1993

Serotonin alters an inwardly rectifying current (Ih) in rat cerebellar Purkinje cells under voltage clamp.

The effects of serotonin (5-HT) on the hyperpolarization-activated sodium-potassium inward current (H-current: Ih) were examined in cerebellar Purkinje cells (PCs) under current- and voltage-clamp conditions. Quasi-steady state current versus voltage relationships under voltage clamp conditions showed that 5-HT decreased the inward rectification at potentials negative to -70 mV with a corresponding decrease in the slope conductance. In 70% of PCs, 5-HT produced dose-related attenuations of the Ih current with corresponding decreases in slope conductances across a range of hyperpolarized potentials. A negative shift in the Ih activation curve was elicited by 5-HT so that the amplitude of Ih current active near rest and at more hyperpolarized ranges was decreased. Serotonin-induced inhibition of Ih shows some receptor subtype selectivity in that DOI, the 5-HT2/IC receptor agonist, most closely mimicked the actions of 5-HT. This study reveals a novel inhibitory action of 5-HT on Ih in cerebellar Purkinje cells which may contribute to direct inhibitory effects of 5-HT on spontaneous firing and modulatory actions on gamma-aminobutyric acid (GABA)-mediated responses to PCs.

Animals↗
PubMed1977

Development of the single microelectrode current and voltage clamp for central nervous system neurons.

The development of a single microelectrode clamping circuit for central nervous system preparations is presented. The efficacy of the circuit in both current and voltage clamp modes is demonstrated by investigating the membrane properties of cat spinal motoneurons. Results are compared with those obtained using conventional techniques and reveal that this technique can be more readily applied to central nervous system neurons. The constraints invovled in employing this system to study time-varying events are also discussed.

Animals↗
PubMed1991

Effects of hypothalamic peptides on electrical activity and membrane currents of 'patch perforated' clamped GH3 anterior pituitary cells.

'Perforated-patch' recordings of rat anterior pituitary GH3 cells allow long and stable monitoring of electrical activity and membrane currents. Under current clamp conditions, the biphasic effect of thryotropin releasing hormone (TRH) consisting of a transient hyperpolarization followed by a longer phase of increased action potential frequency is fully preserved. Somatostatin suppresses action potential activity and antagonizes the second phase of enhanced spiking caused by TRH. Voltage clamp records of isolated currents indicate that TRH affects calcium-dependent potassium currents, but does not alter either voltage-dependent potassium or calcium currents at times and concentrations at which the electrical activity is increased.

Animals↗
PubMed1991

The mechanism of action of peppermint oil on gastrointestinal smooth muscle. An analysis using patch clamp electrophysiology and isolated tissue pharmacology in rabbit and guinea pig.

An investigation of the mechanism of peppermint oil action was performed using isolated pharmacological preparations from guinea pig large intestine and patch clamp electrophysiology techniques on rabbit jejunum. Peppermint oil relaxed carbachol-contracted guinea pig taenia coli (IC50, 22.1 micrograms/mL) and inhibited spontaneous activity in the guinea pig colon (IC50, 25.9 micrograms/mL) and rabbit jejunum (IC50, 15.2 micrograms/mL). Peppermint oil markedly attenuated contractile responses in the guinea pig taenia coli to acetylcholine, histamine, 5-hydroxytryptamine, and substance P. Peppermint oil reduced contractions evoked by potassium depolarization and calcium contractions evoked in depolarizing Krebs solutions in taenia coli. Potential-dependent calcium currents recorded using the whole cell clamp configuration in rabbit jejunum smooth muscle cells were inhibited by peppermint oil in a concentration-dependent manner. Peppermint oil both reduced peak current amplitude and increased the rate of current decay. The effect of peppermint oil resembled that of the dihydropyridine calcium antagonists. It is concluded that peppermint oil relaxes gastrointestinal smooth muscle by reducing calcium influx.

Animals↗
PubMed1995

Freeze clamping musculo-tendinous junctions for in vitro simulation of joint mechanics.

Incorporation of physiologic muscle tensions to simulate normal in vivo joint loading in cadaveric biomechanical studies has been a challenging problem, especially about the knee, foot, and shoulder. Simulation of muscle contraction requires attachment of tension producing devices to musculotendinous units. To this end, we modified the 'cryo-jaw' device, first described by Riemersma and Schamhardt (1982, J. Biomechanics 15, 619-620) to couple linear actuators to fresh cadaver tendons. These clamps were used in the simulation of 11 different muscles in laboratory investigations of shoulder, elbow, knee, and foot function. The clamps were able to transmit repetitively 3500 N of quadriceps force in eight knees and 2000 N of Achilles force in 11 feet. Overall success rate was 95%.

Ankle Joint↗
PubMed1975

Iatrogenic ileal atresia secondary to clamping of an occult omphalocele.

Clamping of an occult omphalocele has led to complete division of an entrapped loop of ileum in two instances. The proximal end has been sealed in the process, producing an iatrogenic ileal atresia. The clinical picture in both instances differed from that usually found with ileal atresia. Escape of a small amount of meconium from the transected cord was noted in one, and the stump of the cord in the other appeared red and engorged. Clamping the umbilical cord routinely at least 5 cm from the abdominal wall is recommended.

Female↗
PubMed1983

Effects of pretreatment with coenzyme Q10 on myocardial preservation during aortic cross clamping.

A protective effect of coenzyme Q10 on the ischemic and reperfused myocardium was investigated in the isolated working rat heart preparation. Rats were treated intraperitoneally with 30 mg/kg coenzyme Q10, daily for 7 days. The controls were given the same dose of the vehicle. After 25 min of equilibration the hearts were made totally ischemic at 35.5 degrees C for 30 min, arrested with high potassium cardioplegic solution immediately after aortic cross clamping. The recovery of cardiac power in the coenzyme Q10 pretreated group was significantly (P less than 0.05) better than that in vehicle pretreated group. Creatine phosphokinase (CPK) release during reperfusion was significantly (P less than 0.05) reduced by the pretreatment of coenzyme Q10. Tissue analysis for high energy phosphate compounds revealed no significant difference between the two groups. Tissue lactate content at 30 min of ischemia was significantly (P less than 0.001) lower in the coenzyme Q10 pretreated group. These results suggest that pretreatment with coenzyme Q10 is effective for reducing ischemic injury caused by aortic cross clamping.

Animals↗
PubMed1993

Effect of OP-41483.alpha-CD, a prostacyclin analog, on a clamp-induced endothelial injury in rats.

We studied the effect of OP-41483.alpha-CD, a stable prostacyclin analog, on clamp-induced endothelial injury in rats. The injury was assessed by vascular Evans blue leakage and using a scanning electron microscope. OP-41483.alpha-CD significantly reduced the Evans blue leakage at doses of 30 and 100 ng/kg/min. PGE1.CD was also found to show an equipotent inhibitory action on the dye leakage. From scanning electron microscopic observations, a moderate degree of intimal defects, microvillous projections and platelet adhesions at the luminal surface were seen in the specimens from OP-41483.alpha-CD (30 and 100 ng/kg/min) treated rats. Furthermore, OP-41483.alpha-CD, PGE1.CD and Dibutyryl cyclic AMP (DbcAMP) were found to accelerate a proliferation of cultured bovine endothelial cells in a dose-dependent manner in vitro. Taken together, these data indicate that the endothelial regenerative effect of OP-41483.alpha-CD could contribute to healing of clamp-induced endothelial injury and it may be an important therapeutic drug to protect vascular intimal injury.

Animals↗
PubMed1984

Comparison of porcine and semisynthetic human insulins using euglycemic clamp-derived glucose-insulin dose-response curves in insulin-dependent diabetes.

In order to compare the biologic effectiveness of porcine and semisynthetic human insulins, a euglycemic clamp method was used in eight insulin-dependent diabetic subjects. Each subject was tested for each insulin on separate days. In order to derive glucose-insulin dose-response curves for both insulins, sequential but constant infusion rates of 0.2, 0.5, 1.0, and 2.0 mU/kg/min were performed. Plasma glucose levels attained during the euglycemic clamp were 96 +/- 3 mg/dL. At each insulin infusion rate, the steady-state glucose infusion rate required to maintain euglycemia was measured. At each increment of insulin infused, steady-state glucose infusion rates for porcine insulin were 1.12 +/- 0.22, 1.90 +/- 0.59, 4.28 +/- 0.61, and 9.37 +/- 0.66 mg/kg/min compared with 1.27 +/- 0.42, 2.38 +/- 0.20, 4.25 +/- 0.43, and 8.87 +/- 0.67 mg/kg/min for semisynthetic human insulin. By ANOVA, no significant difference was noted between the two insulins. Because insulin infusion rates may not result in predictable circulating free insulin levels in subjects who have circulating insulin antibodies, free insulin levels were determined. When steady-state glucose infusion rates were compared with free insulin levels achieved at the four insulin infusion rates, dose-response curves for both porcine and semisynthetic human insulins were virtually identical. These data suggest that semisynthetic human insulin has equivalent biologic effects on overall glucose metabolism compared with porcine insulin in insulin-dependent diabetes.

Adult↗
PubMed1985

Aspects of glucose homeostasis in uremia as assessed by the hyperinsulinemic euglycemic clamp technique.

A three-step hyperinsulinemic euglycemic clamp was performed in 14 nondialyzed uremic and ten age-matched healthy subjects. Nine of the uremics were restudied for a mean of 42 days (range, 21 to 88 days) after initiation of dialysis therapy. Insulin was infused at the following three rates: 0.5 mU X kg-1 X min-1, 2.0 mU X kg-1 X min-1, and 4.0 mU X kg-1 X min-1. Each dose was given for 120 minutes. Glucose uptake during the last 30 minutes of each clamp were consistently lower in uremic patients pre-dialysis than in controls (2.3 +/- 0.3 v 6.6 +/- 0.8 mg X kg-1 X min, 7.8 +/- 0.6 v 13.2 +/- 1.1 mg X kg-1 X min-1 and 9.6 +/- 0.7 v 15.5 +/- 1.0 mg X kg-1 X min-1, all P less than 0.001). Serum insulin levels were similar in the two groups, and blood glucose values during steady state were maintained at 79 +/- 2.77 +/- 2, and 77 +/- 2 mg/100 mL in uremic subjects and at 72 +/- 3, 73 +/- 2, and 75 +/- 2 mg/100 mL in healthy subjects. The insulin levels required to elicit half-maximal biological response in uremics (82 +/- 5 microU/mL) were markedly higher than in controls (54 +/- 8 microU/mL, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

Effects of massive obesity on insulin sensitivity and insulin clearance and the metabolic response to insulin as assessed by the euglycemic clamp technique.

Insulin sensitivity was studied in nine nondiabetic massively obese patients (one male and eight females ages 39.0 +/- 2.7 years, body mass index 47.1 +/- 1) by the euglycemic clamp technique (40 microU/m2/min) and compared to seven lean control subjects (three males and three females, ages 34.8 +/- 2.5 years, body mass index 23 +/- 1.1). Fasting plasma glucose, immunoreactive insulin, and C-peptide concentrations were higher in the massively obese patients than in the controls (P less than 0.025). Following exogenous insulin infusion, immunoreactive glucagon and C-peptide concentrations decreased similarly in the massively obese patients and controls, indicating normal sensitivity of the alpha and beta cell to insulin. Glucose uptake (M) expressed either as mg X min-1 of fat free mass was significantly reduced in the massively obese patients compared to the controls (P less than 0.001). Similarly, the M/I ratio (glucose uptake per unit of insulin) was significantly reduced in the massively obese patients (P less than 0.001). Free fatty acids and glycerol concentrations measured in the fasting state were significantly elevated in the massively obese patients (free fatty acids 678 +/- 51 v 467 +/- 55 mumol/L, P less than 0.05; glycerol 97 +/- 9 v 59 +/- 11 mumol/L, P less than 0.02). The effects of insulin on antilipolysis was assessed by measuring the reductions in free fatty acids and glycerol concentration during the glucose clamp study. Although the absolute levels remained higher in the massively obese patients, inhibition of lipolysis was similar in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxybutyric Acid↗
PubMed1987

In vivo glucose metabolism in the awake rat: tracer and insulin clamp studies.

The goals of this study were twofold: (1) to determine the in vivo dose-response relationship in the conscious, unstressed rat between the plasma insulin concentration and total body glucose uptake, and between plasma insulin and suppression of endogenous glucose production; and (2) to develop a physiologic compartmental model to describe the kinetics of plasma glucose in the rat in the basal state. In order to perform repeat insulin clamp studies in the same rat, chronic catheters were implanted in the aortic arch (via the carotid artery) and in the cardiac atrium (via the jugular vein), exteriorized, and fixed to the back of the skull with a dental cement cap. Insulin was infused at rates of 1.2, 2.4, 4.8, 12, and 24 mU/min.kg, and the plasma glucose was held constant at the basal level by a variable glucose infusion (euglycemic insulin clamp). The resulting steady-state plasma insulin concentrations ranged from 40 to 1,300 microU/mL. The dose-response curve for glucose uptake was sigmoidal in shape: in the basal state, total glucose utilization averaged 6.8 mg/min.kg at an insulin concentration of 9 microU/mL, half-maximal glucose uptake (18.3 mg/kg.min) occurred at a plasma insulin concentration between 70 and 80 microU/mL, and maximal uptake (36.6 mg/kg.min) was seen at an insulin level in excess of 100 microU/mL. Residual endogenous glucose production was evaluated by a prime-continuous infusion of (3-3H)-glucose. The dose-response curve for suppression of endogenous glucose output also was sigmoidal.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Effects of small changes in glucagon on glucose production during a euglycemic, hyperinsulinemic clamp.

The aim of this study was to examine the influence of small changes in glucagon on hepatic glucose production during a euglycemic, hyperinsulinemic clamp. During 1.0 mU/kg.min insulin infusion, euglycemia was maintained by glucose infusion and glucagon was infused at various rates so as to cause plasma glucagon levels to increase, decrease, or remain unchanged. Changes in glucagon were found to be positively associated with changes in glucose production and inversely related to the degree of suppression of tracer or arteriovenous difference determined endogenous glucose production. Thus, animals in which the glucagon levels increased, appeared to have decreased hepatic insulin sensitivity, while animals in which glucagon levels decreased, appeared to have increased insulin sensitivity. In conclusion, since glucagon often declines during a euglycemic hyperinsulinemic clamp, and since small changes in glucagon can have marked effects on the suppression of hepatic glucose output even in the presence of high insulin levels, changes in glucagon should be considered when conclusions regarding hepatic insulin sensitivity are being drawn.

Animals↗
PubMed1991

Effects of bilateral clamping of carotid arteries on hippocampal kindling in rats.

Moderate reduction of cerebral blood flow by bilateral clamping of carotid arteries (BCCA) in pentobarbital anaesthetized Wistar rats induces decreased PO2 and temperature values in vulnerable brain structures such as hippocampus and frontal cortex during the acute phase of clamping. Up to two weeks chronic increased GABA contents in hippocampus, substantia nigra and frontal cortex could be observed. During this time the development of hippocampal kindling was difficult. These results demonstrated an acute and chronic influence of GABA on most vulnerable brain structures which, however, do not lead to ischemic impacts as histological analyses demonstrate.

Animals↗
PubMed1986

Effects of ciguatoxin on current and voltage clamped frog myelinated nerve fibre.

The effects of 0.25 X 10(-9) and 1.25 X 10(-9) g/ml of purified ciguatoxin (CgTX) upon the node of Ranvier of frog isolated nerve fibres were investigated under current and voltage clamp conditions. When added to the external solution, CgTX induced spontaneous action potentials at a frequency of about 100 Hz, which were reversible upon removal of the toxin. Under voltage clamp conditions, CgTX modified neither linear leakage and capacity currents nor K current, but reversibly induced a maintained (late) inward current (IL) during long lasting depolarizations. IL, as well as the peak Na current, was suppressed by tetrodotoxin (300 nM). The steady-state inactivation curve of the Na current showed that a fraction of the current (corresponding to IL) did not inactivate. IL activated and reversed at voltages about 30 mV more negative than the peak Na current (recorded under control conditions or in the presence of CgTX). During a given depolarizing pulse, the amplitude of IL depended on the holding potential. IL was about three times greater when the holding potential was -70 mV rather than -120 mV. We conclude that CgTX specifically interacts with and modifies Na channels. We also conclude that the effects of CgTX depend on membrane potential.

Animals↗
PubMedDate not supplied

Changes in internal ionized Ca2+ and H+ in voltage clamped squid axons.

Squid giant axons were injected with aequorin and tetraethylammonium and were impaled with hydrogen ion sensitive, current and voltage electrodes. A newly designed horizontal microinjector was used to introduce the aequorin. It also served, simultaneously, as the current and voltage electrode for voltage clamping and as the reference for ion-sensitive microelectrode measurements. The axons were usually bathed in a solution containing 150 mM each of Na+, K+, and some inert cation, at either physiological or zero bath Ca2+ concentration [( Ca2+]o), and had ionic currents pharmacologically blocked. Voltage clamp pulses were repeatedly delivered to the extent necessary to induce a change in the aequorin light emission, a measure of axoplasmic ionized Ca2+ level, [( Ca2+]i). Alternatively, membrane potential was steadily held at values that represented deviations from the resting membrane potential observed at 150 mM [K+]o (i.e. approximately -15 mV). In the absence of [Ca2+]o a significant steady depolarization brought about by current flow increased [Ca2+]i (and acidified the axoplasm). Changes in internal hydrogen activity, [H+]i, induced by current flow from the internal Pt wire limited the extent to which valid measurements of [Ca2+]i could be made. However, there are effects on [Ca2+]i that can be ascribed to membrane potential. Thus, in the absence of [Ca2+]o, hyperpolarization can reduce [Ca2+]i, implying that a Ca2+ efflux mechanism is enhanced. It is also observed that [Ca2+]i is increased by depolarization. These results are consistent with the operation of an electrogenic mechanism that exchanges Na+ for Ca2+ in squid giant axon.

Aequorin↗
PubMedDate not supplied

Calcium entry in squid axons during voltage clamp pulses.

Squid giant axons were injected with aequorin and tetraethylammonium and were impaled with sodium ion sensitive, current and voltage electrodes. The axons were usually bathed in a solution of varying Ca2+ concentration ([Ca2+]o) containing 150mM each of Na+, K+ and an inert cation such as Li+, Tris or N-methylglucamine and had ionic currents pharmacologically blocked. Voltage clamp pulses were repeatedly delivered to the extent necessary to induce a change in the aequorin light emission, a measure of axoplasmic Ca2+ level, [Ca2+]i. The effect of membrane voltage on [Ca2+]i was found to depend on the concentration of internal Na+ ([Na+]i). Voltage clamp hyperpolarizing pulses were found to cause a reduction of [Ca2+]i. For depolarizing pulses a relationship between [Ca2+]i gain and [Na+]i indicates that Ca2+ entry is sigmoid with a half maximal response at 22 mM Na+. This Ca2+ entry is a steep function of [Na+]i suggesting that 4 Na+ ions are required to promote the influx of 1 Ca2+. There was little change in Ca2+ entry with depolarizing pulses when [Ca2+]o is varied from 1 to 10mM, while at 50mM [Ca2+]o calcium entry clearly increases suggesting an alternate pathway from that of Na+/Ca2+ exchange. This entry of Ca2+ at high [Ca2+]o, however, was not blocked by Cs+o. The results obtained lend further support to the notion that Na+/Ca2+ exchange in squid giant axon is sensitive to membrane voltage no matter whether this is applied as a constant change in membrane potential or as an intermittent one.

Aequorin↗