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M Naraghi

Publications and source records attributed to M Naraghi.

At least 19 recordsLinked to original sources
PubMed1998

Two-dimensional determination of the cellular Ca2+ binding in bovine chromaffin cells.

The spatiotemporal profile of intracellular calcium signals is determined by the flux of calcium ions across different biological membranes as well as by the diffusional mobility of calcium and different calcium buffers in the cell. To arrive at a quantitative understanding of the determinants of these signals, one needs to dissociate the flux contribution from the redistribution and buffering of calcium. Since the cytosol can be heterogeneous with respect to its calcium buffering property, it is essential to assess this property in a spatially resolved manner. In this paper we report on two different methods to estimate the cellular calcium binding of bovine adrenal chromaffin cells. In the first method, we use voltage-dependent calcium channels as a source to generate calcium gradients in the cytosol. Using imaging techniques, we monitor the dissipation of these gradients to estimate local apparent calcium diffusion coefficients and, from these, local calcium binding ratios. This approach requires a very high signal-to-noise ratio of the calcium measurement and can be used when well-defined calcium gradients can be generated throughout the cell. In the second method, we overcome these problems by using calcium-loaded DM-nitrophen as a light-dependent calcium source to homogeneously and quantitatively release calcium in the cytosol. By measuring [Ca2+] directly before and after the photorelease process and knowing the total amount of calcium being released photolytically, we get an estimate of the fraction of calcium ions which does not appear as free calcium and hence must be bound to either the indicator dye or the endogenous calcium buffer. This finally results in a two-dimensional map of the distribution of the immobile endogenous calcium buffer. We did not observe significant variations of the cellular calcium binding at a spatial resolution of approximately 2 micron. Furthermore, the calcium binding is not reduced by increasing the resting [Ca2+] to levels as high as 1.1 microM. This is indicative of a low calcium affinity of the corresponding buffers and is in agreement with a recent report on the affinity of these buffers (Xu, T., M. Naraghi, H. Kang, and E. Neher. 1997. Biophys. J. 73:532-545). In contrast to the homogeneous distribution of the calcium buffers, the apparant calcium diffusion coefficient did show inhomogeneities, which can be attributed to restricted diffusion at the nuclear envelope and to rim effects at the cell membrane.

Acetates↗
PubMed1998

Two dye two wavelength excitation calcium imaging: results from bovine adrenal chromaffin cells.

We tested a mixture of Calcium-Green-1 (CG-1) and Brilliantsulfaflavine (BS) for dual excitation ratiometric measurements of the intracellular free calcium concentration ([Ca2+]i) in bovine adrenal chromaffin cells. Dyes were coloaded (without being molecularly linked to each other) in the whole-cell configuration of the patch clamp technique. We compared the loading time-courses of CG-1 and BS, investigated their intracellular distribution patterns and studied the time course of photobleaching. We determined the apparent dissociation constant of CG-1, both optically and by potentiometric titration. Our findings indicate that: (i) with excitation at 420/488 nm, calibrated fluorescence signals could be derived using a Grynkiewicz-type equation; (ii) BS is an ideal reference dye that displayed no interaction with CG-1 or cellular constituents; and (iii) that calibration requires diffusional equilibration between pipette and the accessible volume of the cell. Spatially resolved recordings of fluorescence excitation spectra revealed elevated fluorescence of CG-1 in the nucleus such that reported [Ca2+]i levels seemed 25% higher compared to cytosolic values. Comparing fluorescence emission from in vitro dye solutions with in vivo values, we could estimate the accessible volume fraction and amount of Ca(2+)-insensitive dye.

Adrenal Glands↗
PubMed1997

Linearized buffered Ca2+ diffusion in microdomains and its implications for calculation of [Ca2+] at the mouth of a calcium channel.

Immobile and mobile calcium buffers shape the calcium signal close to a channel by reducing and localizing the transient calcium increase to physiological compartments. In this paper, we focus on the impact of mobile buffers in shaping steady-state calcium gradients in the vicinity of an open channel, i.e. within its "calcium microdomain." We present a linear approximation of the combined reaction-diffusion problem, which can be solved explicitly and accounts for an arbitrary number of calcium buffers, either endogenous or added exogenously. It is valid for small saturation levels of the present buffers and shows that within a few hundred nanometers from the channel, standing calcium gradients develop in hundreds of microseconds after channel opening. It is shown that every buffer can be assigned a uniquely defined length-constant as a measure of its capability to buffer calcium close to the channel. The length-constant clarifies intuitively the significance of buffer binding and unbinding kinetics for understanding local calcium signals. Hence, we examine the parameters shaping these steady-state gradients. The model can be used to check the expected influence of single channel calcium microdomains on physiological processes such as excitation-secretion coupling or excitation-contraction coupling and to explore the differential effect of kinetic buffer parameters on the shape of these microdomains.

Adenosine Triphosphate↗
PubMed1997

Kinetic studies of Ca2+ binding and Ca2+ clearance in the cytosol of adrenal chromaffin cells.

The Ca2+ binding kinetics of fura-2, DM-nitrophen, and the endogenous Ca2+ buffer, which determine the time course of Ca2+ changes after photolysis of DM-nitrophen, were studied in bovine chromaffin cells. The in vivo Ca2+ association rate constants of fura-2, DM-nitrophen, and the endogenous Ca2+ buffer were measured to be 5.17 x 10(8) M-1 s-1, 3.5 x 10(7) M-1 s-1, and 1.07 x 10(8) M-1 s-1, respectively. The endogenous Ca2+ buffer appeared to have a low affinity for Ca2+ with a dissociation constant around 100 microM. A fast Ca2+ uptake mechanism was also found to play a dominant role in the clearance of Ca2+ after flashes at high intracellular free Ca2+ concentrations ([Ca2+]), causing a fast [Ca2+]i decay within seconds. This Ca2+ clearance was identified as mitochondrial Ca2+ uptake. Its uptake kinetics were studied by analyzing the Ca2+ decay at high [Ca2+]i after flash photolysis of DM-nitrophen. The capacity of the mitochondrial uptake corresponds to a total cytosolic Ca2+ load of approximately 1 mM.

Acetates↗
PubMed1997

T-jump study of calcium binding kinetics of calcium chelators.

Recent experimental studies have investigated the kinetic competition between calcium chelators and the secretion apparatus at a fast central synapse. Simultaneously, mathematical modelling studies indicate the importance of a quantitative knowledge of the binding kinetics of the chelators in studying fast physiological processes operating on a millisecond time scale. Using the temperature-jump relaxation method, I have studied the in vitro kinetics of Bis-Fura-2, Furaptra, Fluo-3, Calcium-Green-1, Calcium-Green-5N, Calcium-Orange-5N as well as EGTA, BAPTA and H-EDTA in conditions which are identical to those implemented in our patch clamp recordings, i.e. 100-140 mM CsCl, 20-40 mM Cs-HEPES, 8 mM NaCl, pH = 7.2 at 22 degrees C. The results can be summarized as follows: all fluorescent indicators have on rates in the range of 10(8)-10(9) M-1s-1. They differ significantly with respect to their off-rates from each other according to their affinities, ranging from 100 s-1 up to 26,000 s-1. BAPTA is kinetically almost indistinguishable from Fura-2. EGTA and H-EDTA have small binding rate constants for calcium in the range of 3 x 10(6) M-1s-1 since, at pH 7.20, protons need to be dissociated from the chelators before they can bind calcium ions.

Aniline Compounds↗
PubMed1995

Effect of esmolol given during cardiopulmonary bypass on fractional area of contraction from transesophageal echocardiography.

The infusion of esmolol during hypothermic cardiopulmonary bypass (CPB) has no negative myocardial effects after CPB, despite increased esmolol levels during CPB due to hypothermia. The purpose of this randomized, double-blind, prospective study was to measure the effects of esmolol infused during CPB on cardiac function as measured by calculated indices of cardiac work and by transesophageal echocardiography (TEE). Patients scheduled for CPB were randomized to receive intravenous esmolol (300 micrograms.kg-1.min-1 during CPB after bolus of 2 mg/kg prior to CPB) or placebo. Infusion was stopped at 10 min after release of aortic cross-clamp. Hemodynamics and TEE were recorded during the procedure. Fractional area of contraction (FAC), an approximation of left ventricular ejection fraction, was calculated from end-diastolic and end-systolic areas. Esmolol was administered to 15 patients and placebo to 14. Heart rates in the esmolol group were lower during infusion and prior to CPB (P < 0.05). Stroke volume index and left ventricular stroke work index were higher in the esmolol group at 15 min post-CPB (P < 0.05). FAC was higher in the esmolol group at 15 and 30 min post-CPB (P < 0.05), but no difference was observed between groups at 1 h post-CPB. Esmolol infused during CPB in this series of patients was associated with better left ventricular function during the first 0.5 h post-CPB.

Adrenergic beta-Antagonists↗
PubMed1994

Treatment of the cutaneous pain of acute herpes zoster with 9% lidocaine (base) in petrolatum/paraffin ointment.

BACKGROUND: Treatment of the pain of acute herpes zoster by local anesthetic injections has drawbacks. Topical percutaneous local anesthesia (TPLA) may offer another strategy of providing regional analgesia in affected patients. OBJECTIVE: We evaluate the analgesic efficacy and safety of 9% (wt/vol) lidocaine (base) in petrolatum/paraffin ointment in patients with acute herpes zoster. METHODS: Ointment was applied to the affected skin of 22 patients. Pain, tenderness, sensitivity to pinprick and cold, and blood lidocaine concentration were measured repeatedly during a 20-hour interval and intermittently thereafter. RESULTS: Mean pain, tenderness, and cutaneous sensation scores were reduced at measurements taken from 4 to 20 hours after ointment application (p < 0.05), but not every patient obtained relief. No patient had local skin irritation or systemic toxic effects related to the local anesthetic. CONCLUSIONS: TPLA is a promising therapy for control of cutaneous pain of acute herpes zoster. Controlled studies should be performed to prove efficacy, determine optimal TPLA formulation, and define dosage limits.

Acute Disease↗
PubMed1994

Odorant-induced oscillations in the mushroom bodies of the locust.

Kenyon cells are the intrinsic interneurons of the mushroom bodies in the insect brain, a center for olfactory and multimodal processing and associative learning. These neurons are small (3-8 microns soma diameter) and numerous (340,000 and 400,000 in the bee and cockroach brains, respectively). In Drosophila, Kenyon cells are the dominant site of expression of the dunce, DC0, and rutabaga gene products, enzymes in the cAMP cascade whose absence leads to specific defects in olfactory learning. In honeybees, the volume of the mushroom body neurophils may depend on the age or social status of the individual. Although the anatomy of these neurons has been known for nearly a century, their physiological properties and the principles of information processing in the circuits that they form are totally unknown. This article provides a first such characterization. The activity of Kenyon cells was recorded in vivo from locust brains with intracellular and local field potential electrodes during olfactory processing. Kenyon cells had a high input impedance (approximately 1 G omega at the soma). They produced action potentials upon depolarization, and consistently showed spike adaptation during long depolarizing current pulses. They generally displayed a low resting level of spike activity in the absence of sensory stimulation, despite a large background of spontaneous synaptic activity, and showed no intrinsic bursting behavior. Presentation of an airborne odor, but not air alone, to an antenna evoked spatially coherent field potential oscillations in the ipsilateral mushroom body, with a frequency of approximately 20 Hz. The frequency of these oscillations was independent of the nature of the odorant. Short bouts of oscillations sometimes occurred spontaneously, that is, in the absence of odorant stimulation. Autocorrelograms of the local field potentials in the absence of olfactory stimulation revealed small peaks at +/- 50 msec, suggesting an intrinsic tendency of the mushroom body networks to oscillate at 20 Hz. Such oscillatory behavior could not be seen from local field potential recordings in the antennal lobes, and may thus be generated in the mushroom body, or via feedback interactions with downstream neurons in the protocerebrum. During the odor-induced oscillations, the membrane potential of Kenyon cells oscillated around the resting level, under the influence of excitatory inputs phase-locked to the field activity. Each phasic wave of depolarization in a Kenyon cell could be amplified by intrinsic excitable properties of the dendritic membrane, and sometimes led to one action potential, whose timing was phase-locked to the population oscillations.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Outpatient spinal opiate analgesia: a case report.

Outpatient spinal opiate analgesia for relief of cancer pain has been well-described in the literature. We report a case of a patient with metastatic disease who received epidural morphine using a subcutaneous epidural catheter via home injections. The patient and his family administered the medications. There are several options to choose from when using epidural morphine, and each patient's needs must be evaluated for the appropriate system.

Analgesia, Epidural↗
PubMed1992

Elective transtracheal jet ventilation for bronchoscopic removal of tracheal foreign body.

We have shown that transtracheal jet ventilation can be used safely and effectively when removing a foreign body from the airway. In some cases, it may be wise to choose this method of ventilation initially, thus avoiding the difficulties associated with more conventional modes of controlled ventilation. This is especially true when the potential for loss of the airway during the procedure is significant. This technique also allows the bronchoscopist the benefit of unimpeded access to the airway and adequate uninterrupted time for his operative procedure.

Bronchoscopy↗
PubMed1988

Complications of endotracheal intubation.

Tracheal intubation for airway control, once done only by anesthesiologists during surgical procedures, is now being done by physicians in other specialties and by nurses, technicians, and paramedics in areas other than the operating room. Intubation, however, does not always assure a patent airway. Unrecognized esophageal placement of endotracheal tubes is the major cause of cardiac arrest and brain damage associated with intubation. Though auscultation for breath sounds is the universally accepted method of verifying proper tube placement, recent studies indicate that it is reliable only approximately two thirds of the time in situations in which verification of proper placement is needed most and is least obvious. The usefulness of this technique merits reassessment. Identification of carbon dioxide in end-expired air is the most reliable method for verification, but instruments to detect carbon dioxide are usually immediately available only in special care and surgical suites. Mouth-to-tube insufflation with a two-way disposable microbial filter differentiates immediately between esophageal and tracheal placement and can be used in any area. Malpositioned and malfunctioning tubes cause partial or complete obstruction accompanied by varying degrees of hypoxemia and hypercapnia. Respiratory and circulatory derangements and brain damage ensue if the problem is not promptly recognized and corrected. We discuss the most common causes of tube malfunction.

Airway Obstruction↗
PubMed1984

Chronic neuralgia incidence following local anesthetic therapy for herpes zoster.

We treated 72 patients, referred to a pain clinic for acute herpes zoster neuralgia, with local anesthetics administered by nerve block and infiltration. Only those patients with severe pain initially proved to be at risk for the development of chronic postherpetic neuralgia (defined as pain in the involved dermatomes lasting at least six months). Although local anesthetic injections effectively relieved the acute pain of active herpes zoster, they did not prevent the development of chronic postherpetic neuralgia.

Acute Disease↗
PubMed1979

Adverse effects of pancuronium in patients with hemorrhagic shock.

Thirty-five patients with hemorrhagic shock had surgical repair of trauma to the great vessels using a ketamine-pancuronium-nitrous oxide sequence for anesthesia. The data of the cardiovascular and respiratory changes occurring during anesthesia and the operation were tabulated and subjected to multifactorial computer analysis. Fifteen patients died during or after operation because the injury was beyond repair. Twenty survived the oepration. Profound hypotension associated with mild tachycardia occurred with surprising regularity each time incremental doses of pancuronium were administered in nearly all patients. This hypotension was not associated with the administration of any other drug or with any other parameter and strongly implicates pancuronium as the causative factor. Pancuronium should be used cautiously and administered in small increments to this type of patient if it is used as a muscle relaxant.

Anesthesia, Endotracheal↗