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  • 1
    Electronic Resource
    Electronic Resource
    Thyroid follicular cells: the resting membrane potential and the communication network (1981)
    Springer
    Pflügers Archiv 391 (1981), S. 119-124 
    Details
    ISSN: 1432-2013
    Keywords: Thyroid gland ; Follicular cell ; Membrane potential ; Membrane resistance ; Cell to cell coupling ; Specific membrane resistance ; Electrogenic pump
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Intracellular recordings of membrane potential, input resistance and time constant have been made in vitro from the follicular cells of the rat, rabbit and guinea-pig thyroid glands using glass microelectrodes. The passive permeability properties of these cells have been investigated by altering the concentration of one or more ions in the superfusing fluid. Investigations into the intercellular coupling characteristics of the thyroid gland were made by inserting two microelectrodes into neighbouring communicating cells. The mean transmembrane potentials were between −60 and −70 mV in all three species studied. The magnitude of the membrane potential in the rat was found to be dependent mainly upon the gradient for potassium (K+) across the membrane. Current-voltage relationships were investigated in all three species by injecting rectangular de- or hyperpolarizing current pulses through the recording microelectrode. Within a relatively wide range (−20 to −80 mV), there was an approximately linear relationship between injected current and change in membrane potential. The input resistance was about 11 MΩ in all three species, while the time constant (τ) varied from 5–35 ms. Readmitting K to K-deprived rat thyroids during intracellular microelectrode recording caused a transient hyperpolarization which was unaccomapanied by any change in input resistance. The transient hyperpolarization was abolished by ouabain. Addition of 10−3 M ouabain to the resting cell caused an immediate depolarization of approximately 2 mV. Electrical coupling between neighbouring cells could only be observed if the distance between the tips of the two exploring microelectrodes was less than 15 μm. The coupling coefficient (V 2/V 1) was close to 1. Assuming uniform current spread within one follicle and electrical isolation of individual follicles from each other the specific membrane resistance of the rat thyroid follicular cells was calculated to be 4.9 kΩcm2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00657001
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Nervous control of membrane conductance in mouse lacrimal acinar cells (1984)
    Springer
    Pflügers Archiv 400 (1984), S. 51-59 
    Details
    ISSN: 1432-2013
    Keywords: Lacrimal acinar cell ; Membrane potential ; Membrane resistance ; Nerve stimulation ; Electrical field stimulation ; Acetylcholine ; Adrenaline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Intracellular microelectrode recordings were made from superfused in vitro preparations of mouse lacrimal giand. The lacrimal acinar cell had a mean resting membrane potential of −44.1±0.5 mV and a mean input resistance of 3.5±0.15 MΩ. Electrical field stimulation (FS) had similar effects to ACh applied by microionophoresis, both evoking a biphasic membrane hyperpolarization (up to 15 mV) accompanied by a reduction in input resistance. The equilibrium potential values (EFS and EACh) for the responses to brief duration FS and ACh ionophoresis ranged between −45 and −75 mV and depended on the time at which measurements were made following the onset of stimulation. Superfusion of ACh or adrenaline also caused membrane hyperpolarization and increased membrane conductance. Estimations of EFS and EACh made during prolonged periods of FS and ACh superfusion yielded mean values of −53.9±1.9 mV and −53.4±1.5 mV respectively. FS evoked a response in all preparations tested with maximal effects seen at 40 Hz frequency. The mean latency of the FS-evoked hyperpolarization (40 Hz) was 270±21 ms and that for the ACh ionophoretic response was 400±65 ms. Low frequency FS (0.5–5 Hz) also induced membrane hyperpolarization and responses to single shock stimuli were occasionally observed. The FS-evoked hyperpolarization was abolished following the blockade of nerve conduction by superfusion of either Na-free or tetrodotoxin-containing media. Effects of FS were not seen in the presence of atropine. Neostigmine potentiated the FS- and ACh-evoked hyperpolarizations. Spontaneous miniature hyperpolarizations were unaffected by tetrodotoxin but abolished by atropine. It is concluded that FS excites a well developed cholinergic innervation of the mouse lacrimal gland resulting in ACh release and acinar cell hyperpolarization. ACh, which appears to be the only neurotransmitter released, mediates its effects by increasing plasma membrane permeability to mainly K ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00670536
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  • 3
    Electronic Resource
    Electronic Resource
    Amino acid-evoked membrane potential and resistance changes in pancreatic acinar cells (1980)
    Springer
    Pflügers Archiv 386 (1980), S. 153-159 
    Details
    ISSN: 1432-2013
    Keywords: l-Amino acids ; Membrane potential ; Membrane resistance ; Pancreatic acinar cell ; Na-conductance ; l-Alanine-amino acid interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect of some neutrall-amino acids, alanine, valine and proline, on the pancreatic acinar cell membrane potential and resistance was investigated. Simultaneous recordings were made with two intracellular microelectrodes on isolated superfused segments of mouse pancreas. Amino acids were applied by inclusion at known concentrations in the superfusion fluid or by microionophoresis from extracellular micropipettes. l-Alanine (10 mmol·l−1) evoked a maximal membrane depolarization of about 18 mV. A just detectable depolarization was observed at 0.1 mmol·l−1 (3 mV). Halfmaximal depolarization was observed at 1.6 mmol·l−1.d-Alanine had virtually no effect. Microionophoretic applications ofl-alanine,l-valine orl-proline evoked depolarization and resistance reduction with a very short delay (〈50 ms). The dose response curves for depolarization and resistance reduction were similar. The amplitude of the depolarization evoked byl-alanine,l-valine andl-proline depended linearly on the level of the pre-set membrane potential (membrane potential could be changed by direct current injection). With decreasing intracellular negativity there was a decrease in the size of the amino acid-evoked depolarization. When the membrane potential was inside positive the amplitude became very small. Extrapolation of the linear relations between membrane potential and size of depolarization revealed a null potential of +20 to +45 mV. Thel-alanine-evoked depolarization was acutely reduced but not abolished by replacing extracellular Na by Tris or Li. l-Alanine,l-proline andl-valine exhibited mutual inhibition of evoked depolarization even when the depolarizing effect of the first applied amino acid was balanced by direct current injection. It is concluded that severall-amino acids act on the pancreatic acinar plasma membrane by opening conductance pathways mainly permeable to Na.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00584203
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of intracellular EGTA injection on stimulant-evoked membrane potential and resistance changes in pancreatic acinar cells (1980)
    Springer
    Pflügers Archiv 386 (1980), S. 147-152 
    Details
    ISSN: 1432-2013
    Keywords: Pancreatic acinus ; Calcium ; Membrane potential ; Membrane resistance ; EGTA ; Stimulus-permeability coupling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Membrane potential and resistance were measured from two neighbouring electrically coupled cells within the same mouse pancreatic acinus, using one electrode filled with KCl and another filled with K-EGTA [ethylene glycol-bis-(β-amino ethyl ether) N,N′-tetra acetic acid] or K-acetate. EGTA was injected into one cell by passing pulses of hyperpolarizing current through the EGTA microelectrode. In order to ensure constant membrane potential, pulses of depolarizing current of the same intensity were simultaneously passed through the other electrode. Intracellular injection of EGTA, but not acetate, decreased significantly the membrane response (depolarization, resistance reduction) of both coupled cells to small microionophoretic pulses of ACh stimulation. Responses to larger doses were decreased to a smaller extent. Intracellular injection of EGTA also decreased significantly the membrane response of both coupled cells to microionophoretic pulses of pentagastrin stimulation. In contrast intracellular injection of EGTA did not inhibit membrane response tol-alanine stimulation.l-Alanine-evoked membrane depolarization was independent of external Ca. This is in contrast to what has previously been shown for secretagogue effects. It is concluded that EGTA-induced sequestration of cytosolic Ca2+ decreases membrane responses to both ACh and pentagastrin, providing new evidence of the crucial role played by internal Ca2+ in mediating stimulus-permeability coupling. In contrast,l-alanine action does not appear to be mediated by internal Ca2+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00584202
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  • 5
    Electronic Resource
    Electronic Resource
    Separate activation sites for cholecystokinin and bombesin on pancreatic acini (1979)
    Springer
    Pflügers Archiv 382 (1979), S. 263-267 
    Details
    ISSN: 1432-2013
    Keywords: Pancreatic acinar cells ; N2, O2′ dibutyryl guanosine 3′:5′-Monophosphate ; Cholecystokinin antagonist ; Bombesin ; Membrane potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of dibutyryl cyclic guanosine 3′:5′ monophosphate (dbcGMP) on the electrical responses of in vitro mouse pancreatic acinar cells to caerulein, bombesin and acetylcholine, applied by microionophoresis, were investigated using intracellular microelectrode recordings. Exposure to dbcGMP (10−3 mol ·l−1) quickly abolished the depolarization response to caerulein ionophoresis, while the bombesin-nonapeptide and acetylcholine-induced depolarizations were retained. Exposing acinar cells to 2×10−4 mol·l−1 dbcGMP reduced their sensitivity such that a 10-fold increase in the applied caerulein ionophoresis current was required to restore the responses to the same magnitude as those obtained in a dbcGMP-free environment. The response to topical applications of pentagastrin and CCK-33 were also abolished by dbcGMP. The results provide direct evidence that functional ACh, bombesin and CCK receptors are all present within the same acinar cell unit. The dbcGMP-induced inhibition of responses evoked by CCK-like peptides is immediate, specific and easily reversible. DbcGMP acts as a competitive antagonist of the CCK receptor on pancreatic acinar cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00583711
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    Paper (German National Licenses)
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