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J O'Doherty

Publications and source records attributed to J O'Doherty.

28 records · Page 2Linked to original sources
PubMed1982

Effect of ionophore A23187 on cytosolic Ca2+ and enzyme secretion.

As the ionophore A23187 is believed to act by increasing cytosolic Ca2+ ([Ca]i), it offers a mechanism for experimentally controlling [Ca]i. Ca2+-selective microelectrodes were employed to examine the effect of A23187 on [Ca]i and the role of [Ca]i in acinar secretion. The mean [Ca]i in acinar cells of the mouse pancreas was determined to be 0.43 +/- 0.03 microM. When the ionophore was added to the saline bathing the acinar cells, 10(-6) M A23187 depolarized the membrane potential (Em) by 5.2 +/- 0.3 mM and the intracellular Ca-electrode potential (ECs) by 9.8 +/- 0.6 while 10(-5) M A23187 depolarized Em by 7.4 +/- 0.3 mV and ECs by 14.1 +/- 0.8. These changes in potentials reflect an increase in [Ca]i to 0.62 +/- 0.03 microM with 10(-6) M and 0.73 +/- 0.05 microM with 10(-5) M A23187. The increase in [Ca]i observed with 10(-6) M A23187 was similar to that found with concentrations of acetylcholine (Ach) that produced maximal enzyme secretion, whereas the increase in [Ca]i with 10(-5) M was similar in magnitude to that observed with ACh concentration that inhibited or reduced secretion. Measurements of amylase release during 30 min exposure of A23187 produced an 88.4% increase in amylase activity over basal levels with 10(-6) M and little or no change with (10(-5) M, indicating that the ionophore influences secretion through changes in [Ca]i in a manner analogous to the natural secretagogue ACh. This report establishes that acinar secretion occurs only within a narrow range of [Ca]i activities and suggests intracellular increases in both "bound" and "free" calcium may occur during cell activation.

Acetylcholine↗
PubMed1982

Intracellular Na+ and K+ activities during insulin stimulation of rat soleus muscle.

The action of insulin on the resting membrane potential (Em) and intracellular sodium and potassium activities (aNa, aK) of rat soleus muscle fibers was determined by direct intracellular measurements of aNa, aK, and Em using Na-selective, K-selective, and conventional microelectrodes. The use of these microelectrodes allowed us to continuously monitor these parameters in the same fiber. Although we were able to accurately measure aNa and aK and continuously monitor their levels throughout periods of insulin stimulation of up to 20 min duration, we were unable to detect any significant change in Em, aNa, or aK. Varying the concentration of insulin or extracellular glucose failed to alter our observations. These results indicate that the action of insulin on the sarcolemma and subsequent increase in glucose transport must result from some mechanism independent of a change in membrane potential or intracellular sodium or potassium activity.

Animals↗
PubMed1982

Stimulation of pancreatic acinar secretion: increases in cytosolic calcium and sodium.

Na+-selective and Ca2+-selective microelectrodes were used to examine the ionic mechanisms regulating acetylcholine (ACh) stimulation of pancreatic secretion. The cytosolic concentrations of free ionized Na+ and Ca2+ ([Na]i, [Ca]i) were determined in unstimulated acinar cells to be 10.5 +/- 0.4 mM and 0.43 +/- 0.03 microM, respectively. By measuring the induced changes in intracellular Ca2+, Na+, and membrane potentials (ECa, ENa, Em), we were able to demonstrate that 5 X 10(-8) M ACh depolarized Em by 4.3 +/- 0.2 mV and increased [Na]i and [ca]i to 12.2 +/- 0.3 mM and 0.58 +/- 0.02 microM, respectively. Stimulation with ACh at concentrations ranging from 10(-8) to 10(-5) M increased [Ca]i from 0.4 microM to between 0.5 and 1.0 microM. Amylase release reached a maximum at 10(-7) M ACh stimulation and progressively decreased at higher concentrations of stimulus. Increasing the stimulus above an optimal concentration appears to reduce or inhibit enzyme release. These experiments provide direct evidence supporting the concept that acinar cell secretion is triggered by increases in [Ca]i and of calcium's ability to act as primary intracellular mediator. Stimulation after removal of extracellular Ca2+ eliminated the increase in [ca]i that is usually observed in secreting cells, while producing the normal depolarization of Em and increase in [Na]i. These studies demonstrate the increases in [Ca]i are derived from an increase in membrane permeability to Ca2+ and the ability of ACh to depolarize the Em by a transmembrane movement of Na+ that is independent of the change in intracellular Ca2+.

Acetylcholine↗
PubMed1981

Transmembrane and transepithelial movement of calcium during stimulus-secretion coupling.

Electrophysiological studies were undertaken to determine the transmembrane and transepithelial changes in free Ca2+ concentration that occur during serotonin-induced secretion in the salivary glands of the blowfly, Phormia regina. Ca-selective and conventional microelectrodes were used to measure intracellular and luminal Ca2+ concentrations ([Ca]L), serosal membrane and transepithelial potentials (Em, Etr), and their changes during serotonin (5-hydroxytryptamine, 5HT)-induced salivary secretion. The effect of stimulus concentration on these parameters and enzyme release was also determined. Previous studies provided evidence that serosal stimulation with 10(-8) M 5HT caused a hyperpolarization of Em and short phasic two- to threefold increases in [Ca]i. In these studies, higher concentrations of 5HT (10(-7) M) resulted in depolarization of Em by 13 +/- 1.2 mV and of ECa by 64 +/- 2.1 mV, a dramatic increase in [Ca]i, and a decrease in enzyme release. In addition, serotonin (10(-8) M) reduced the normal spontaneous Etr (+19.6 +/- 1 mV) to near zero while causing an increase in [Ca]L from 1.3 +/- 0.3 X 10(-5) mM to 2.0 +/- 0.1 X 10(-3) mM, a concentration isomolar with that of the bathing medium. These results provide direct electrochemical evidence that, during stimulus-secretion coupling of the salivary epithelial cells, the neurohormone serotonin controls the secretory response by the regulation of intracellular Ca2+ and induces transepithelial transport of Ca2+, thereby suggesting that, during secretion, the neurohormone causes the salivary gland to behave as a "leaky epithelium" by activating the paracellular shunt pathways.

Animals↗
PubMed1980

Calcium regulation during stimulus-secretion coupling: continuous measurement of intracellular calcium activities.

Accurate measurements of intracellular calcium activities in salivary gland epithelial cells of the insect Phormia regina were obtained with microelectrodes in which N,N'-di(11-ethoxycarbonyl)undecyl-N,N'-4,5-tetramethyl-3,6-dioxaoctane diacid diamide wsa incorporated in a liquid membrane system. When calibrated in solutions approximating the ionic concentration of the cell interior, these microelectrodes gave rapid stable responses that were linear functions of the logarithm of calcium activities and were not affected by potassium, sodium and magnesium. Continuous monitoring of calcium activities during serotonin-induced saliva release provided direct evidence of hormonal influence on transmembrane calcium movement and spontaneous regulation of intracellular calcium by stimulated cells.

Animals↗
PubMed1980

The palatability of colloidal bulk forming agents.

The palatability of three bulk additives was studied in volunteers under 40 and over 60 years of age. Women highly significantly preferred Normacol Special (Norgine) to Fybogel (Reckitt & Colman) and Celevac Granules (W.B.P.). On both preference and palatability score Normacol Special was significantly preferred to Celevac Granules, as it was in the under 40's on palatability score and in the over 60's on preference, but in the latter, sex may have accounted for the difference observed. Volunteers under the age of 40 gave Celevac a significantly higher palatability score than Fybogel; the reverse occurred in the over 60's. These results have therapeutic implications in patients with different gastro-intestinal disorders.

Adult↗
PubMed1980

Insulin does not act by causing a change in membrane potential or intracellular free sodium and potassium concentration of adipocytes.

The influence of insulin on the intracellular free sodium and potassium ion concentrations ([Na+]i, [K+]i) and resting membrane potential of rat epididymal adipocytes was examined to determine its potential for mediating insulin's action on other cellular processes. Direct intracellular measurements of [Na+]i, [K+]i, and the resting membrane potential were made using ion-selective and conventional microelectrodes. The use of these microelectrodes enabled us to continuously monitor these parameters in the same cell before, during, and after periods of insulin stimulation of up to 20-min duration. The electrical potentials measured in these experiments remained unchanged when the cells were stimulated with insulin (0.01, 0.1, or 1.0 mU/ml). Varying the extracellular glucose concentration had no effect on these results. Our results provide the first direct measurement of [Na+]i and [K+]i in adipose tissue and clearly demonstrate that the response to insulin's association with its receptors on the cell surface and subsequent action on hexose transport and cellular metabolism does not involve a change in membrane potential or intracellular sodium and potassium ions.

Adipose Tissue↗
PubMed1979

Sodium-selective liquid ion-exchanger microelectrodes for intracellular measurements.

The sodium-selective ligand 1,1,1-tris[1(1)-(2(1)-oxa-4(1)-oxo-5(1)-aza-5(1)-methyl)dodecanyl]propane dissolved in 3-nitro-o-xylene containing a small amount of the lipophilic anion tetrachlorophenyl borate was used as a liquid ion-exchanger in sodium-selective microelectrodes. The microelectrodes gave rapid, stable responses that were linear functions of the logarithm of sodium activity. They were tested under conditions approximating those to be expected in the cell interior, and the results indicated that they can be used to measure intracellular sodium activity without significant interference from intracellular potassium.

Animals↗
PubMedDate not supplied

Validating radiation sterilization.

There are three aspects that manufacturers must address when validating radiation sterilization. These are the minimum dose that ensures sterility, the maximum dose at which radiation affects the functionality of the device, and the dose distribution throughout the product. This article defines a validation protocol that satisfies current radiation sterilization standards.

Equipment and Supplies↗