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  • 1
    Electronic Resource
    Electronic Resource
    Contributions of various ions to the resting and action potentials of crayfish medial giant axons (1971)
    Springer
    The journal of membrane biology 5 (1971), S. 345-365 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The membrane of crayfish medial giant axons is permeable at rest to ions in the rank K〉Na〉Ca〉Cl. With K present, variation of the other ions has little or no effect, but with K absent the axon hyperpolarizes when Na is reduced or eliminated by replacement with Tris (slope ca. 30 mV/decade Na0). The hyperpolarization is independent of the presence of Cl or its absence (substitution with methanesulfonate or isethionate). The resistance increases progressively as Na is removed. These changes persist after the spike is blocked with tetrodotoxin. An increase in Ca causes depolarization (slope ca. 20 mV/decade) provided K, Na and Cl are all absent, but in the presence of Cl there is little or no change in membrane potential on increasing Ca to 150mm. The depolarization induced by Ca is associated with an increased resistance. Spike electrogenesis involves Ca activation as well as Na activation, but the after-depolarization at the end of the spike is due to a conductance increase for Ca. Two alternative equivalent circuits for the resting and active membrane are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01957351
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  • 2
    Electronic Resource
    Electronic Resource
    Slowing of the time course of the excitation of squid giant axons in viscous solutions (1979)
    Springer
    The journal of membrane biology 47 (1979), S. 303-325 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The time course of excitation of intracellularly perfused squid giant axons was slowed as the solution viscosity was raised by adding neutral molecules, i.e., glucose and glycerol. By twofold increase of the solution viscosity, the duration of action potential was prolonged to 2.7-fold and the maximum rate of rise decreased to one-half. At the same time, the membrane resistance at resting state increased by 60%. These effects were reversible. The time course of inward and outward currents was slowed also. When the solution viscosity increased to twofold, the time to peak inward current increased by 80%, and the amplitudes of peak inward and steady outward currents decreased by 60% and by 70%, respectively. These effects were not specific for the sodium or the potassium channel. Effects of solution viscosity occurred in both hypotonic and hypertonic solutions. Q10 values of temperature dependence of the time course of the action potential were equal in any viscous solutions. These effects in viscous solutions were explained by the change in solution viscosity but not by the change in solution osmolarities, ionic activities, or solution resistivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869083
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of an outward water flow on potassium currents in a squid giant axon (1983)
    Springer
    The journal of membrane biology 75 (1983), S. 33-44 
    Details
    ISSN: 1432-1424
    Keywords: squid giant axon ; potassium channel ; water flow ; osmotic gradient ; rectification ; channel pore
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The excitation of the squid giant axon was analyzed under an outward water flow through the membrane produced by an osmotic gradient. The outward water flow made an undershoot of the action potential larger by about 25 mV without decreasing its peak largely. It also madeE K more negative but notE Na. The effect of the outward water flow was specific for the potassium channel. The outward current increased and its decline during a long-lasting depolarization became less prominent under the outward water flow. At the same time, inward tail currents for the potassium channel decreased extraordinarily without a large change in the time course. The potassium conductance had a marked rectification in the direction of the water flow. The undershoot of the action potential under the outward water flow was very sensitive to potassium ions in the external solution. Eightmm KCl was effective to diminish the undershoot and to restore the change inE K by about 60% but gave no effect on the reduced tail current. The outward water flow effect can be explained not only by the change in a local concentration of potassium ions at the mouths of the potassium channel due to a sieving but also by the rectification in a hydrodynamic manner.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870797
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  • 4
    Electronic Resource
    Electronic Resource
    Intracellular binding of cationized ferritin prolongs the time course of sodium channel inactivation in squid giant axons (1986)
    Springer
    The journal of membrane biology 89 (1986), S. 75-83 
    Details
    ISSN: 1432-1424
    Keywords: sodium channel ; inactivation ; cationized ferritin ; cytoplasmic surface ; surface charge ; anionic sites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Cationized ferritin (CF) applied intracellularly in squid giant axons bound to the negatively charged sites on the cytoplasmic surface of the axolemma. Under the electron microscope, the distribution of CF was found to be dense and uniform over the axolemmal surface. However, the effect of CF on the membrane excitability was highly specific, the major effect being a prolonging of the inactivation time course of the sodium channel without altering the properties of the potassium channel. The binding of CF did not alter the surface potential related to the membrane excitability. When CF was present intracellularly, the time course of the inactivation was characterized by two time constants (slow and fast). The slow component increased with an increase in CF binding and its time constant had a unique value (26 msec) irrespective of the duration of perfusion and concentration of CF. The concentration of CF at which the half-maximum response occurred was about 150nm. Poly-l-glutamate, charged negatively at neutral pH, removed CF from the axolemma and counteracted the CF effect on the sodium channel, although this poly-acidper se did not affect the membrane excitability. Our results indicate that CF binds electrostatically to the inactivation site of the sodium channel but does not affect the voltage sensor, which is supposed to be located deep in the channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870897
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  • 5
    Electronic Resource
    Electronic Resource
    Single calcium-activated potassium channel in cultured mammary epithelial cells (1989)
    Springer
    Pflügers Archiv 414 (1989), S. 118-124 
    Details
    ISSN: 1432-2013
    Keywords: Mammary epithelial cells ; Patch clamp ; K+ channel ; Ca2+ activation ; Na+ block ; A23187 ; Inward rectification ; Epidermal growth factor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The properties of Ca2+-activated K+ channels in mouse mammary epithelial cells in primary culture were studied by the patch-clamp technique. In cell-attached patches, spontaneous channel openings were sometimes observed; the slope conductance of the currents was about served; the slope conductance of the currents was about 12 pS at negative membrane potentials with a physiological solution (152 mM Na+, 5.4 mM K+) in the pipette. External application of A23187, a calcium ionophore, activated this channel. In excised inside-out patches, the channel was activated by increasing the internal Ca2+ concentration (10−7 to 10−6 M). No voltage dependence of the channel activity was observed. Internal Na+ blocked the outward K+ current in a voltage dependent manner and this block led to the non-linear I–V relationship at positive membrane potentials. The channel was blocked by internal Ba2+ (0.1 mM) and tetracthylammonium (TEA+, 20–50 mM). Ba2+ reduced the open probability but not the single channel conductance, whereas TEA+ reduced the single channel conductance. The single channel conductance of this channel, measured from the inward current with a high-K+ solution (150 mM K+) in the pipette, was large (about 40 pS), and showed inward rectification. These results suggest that this channel is different from the usual small conductance Ca2+-activated K+ channels observed in many other cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00580952
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  • 6
    Electronic Resource
    Electronic Resource
    Involvement of P2-purinergic receptors in intracellular Ca2+ responses and the contraction of mammary myoepithelial cells (1997)
    Springer
    Pflügers Archiv 435 (1997), S. 1-8 
    Details
    ISSN: 1432-2013
    Keywords: Key words Intracellular calcium ; Fura-2 ; Myoepithelial cells ; Oxytocin ; Purinergic receptor ; Mammary gland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Mammary myoepithelial cells were isolated and cultured to characterize their properties. The intracellular calcium concentration (Cai 2+) was measured using the ratio of fura-2 fluorescence at 340 nm to that at 360 nm (F 340/F 360), and the contraction was simultaneously monitored by the change of fluorescence intensity at 360 nm (F 360). Cultured myoepithelial cells retained their contractile machinery as in the intact tissue. NBD-phallacidin fluorescence, which marks F-actin, and electron microscopy showed abundant bundles of microfilaments in the cytoplasm. Oxytocin (〉 0.1 nM) induced an increase in Cai 2+ and contraction. The amplitude and time course of the Cai 2+ increase were not markedly affected in the Ca2+-free solution. Nifedipine (10 μM) did not affect the response to oxytocin. ATP (〉1 μM) induced an increase in Cai 2+ and contraction. The response to ATP was not affected by Ca2+ removal, but was suppressed by suramin (100 μM), an antagonist of P2-purinergic receptors. The order of potency of nucleotides to increase Cai 2+ was ATP = ADP 〉 UTP 〉 UDP. These findings indicate the presence of P2-purinergic receptors in mammary myoepithelial cells. The results suggest that stimulant-induced Cai 2+ increases and contractions are due to release of Ca2+ from intracellular stores in these cells. In addition to the hormonal action of oxytocin, extracellular nucleotides may function as paracrine agents to contract myoepithelial cells in the mammary gland.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050477
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  • 7
    Electronic Resource
    Electronic Resource
    Spontaneous calcium oscillations and mechanically and chemically induced calcium responses in mammary epithelial cells (1993)
    Springer
    Pflügers Archiv 422 (1993), S. 295-304 
    Details
    ISSN: 1432-2013
    Keywords: Intracellular calcium oscillation ; Fura-2 ; Mammary epithelial cells ; Purinergic receptor ; Mechanical response ; Calcium wave ; Bradykinin ; LaCl3
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Changes of intracellular calcium activity (Ca i 2+ ) in mouse mammary epithelial cells in primary culture (normal) and in an established cell line (MMT060562, cancerous) were investigated by microfluorometry and image analysis of fura-2 fluorescence. In both types of cells, some populations exhibited occasional Ca i 2+ oscillations with a period of 50–160 s. Slight mechanical stimulation of a cell with a fine glass pipette induced a Ca i 2+ increase, which spread from the stimulated cell to the surrounding cells with a speed of 7–12 μm/s. ATP (〉1 μmol/l) and ADP, but not AMP induced a Ca i 2+ increase in both cell types. Bradykinin was highly effective (〉 10 nmol/l) only in the cancerous mammary epithelial cells. In Ca2+-free solution, all these Ca i 2+ responses remained unchanged at the first application, and decreased abruptly at the second trial. La3+ (〉0.5 mmol/l) suppressed the response to ATP but not the response to bradykinin. Addition of extracellular Mn2+ rapidly quenched the fura-2 fluorescence in the cell even in a non-stimulated state. Influx of Mn2+ did not increase during Ca i 2+ responses. These results indicate that the sources of Ca i 2+ responses in mammary epithelial cells are intracellular stores, which exchange Ca2+ with the extracellular medium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374284
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  • 8
    Electronic Resource
    Electronic Resource
    The increase in the intracellular Ca2+ concentration induced by mechanical stimulation is propagated via release of pyrophosphorylated nucleotides in mammary epithelial cells (1994)
    Springer
    Pflügers Archiv 427 (1994), S. 533-542 
    Details
    ISSN: 1432-2013
    Keywords: Intracellular calcium ; Fura-2 ; Mammary epithelial cells ; Mechanical stimulation ; Purinoceptor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Mechanical stimulation of one mammary tumor cell in culture induced an increase in its intracellular calcium concentration which spread to surrounding cells. The increase in calcium can also be induced by addition of a solution in which cultured mammary tumor cells were stimulated by repeated pipetting (solution after pipetting cells, SAPC). The activity of the SAPC was completely abolished by treatment with snake venom phosphodiesterase or pyrophosphatase. Uridine triphosphate (UTP), uridine diphosphate (UDP) and ATP (1 μM each) were detected in the SAPC, whereas 5′-UMP and 5′-AMP were produced by phosphodiesterase digestion. A mixture of UTP, UDP and ATP (1 μM each) elicited a calcium response which was comparable to that induced by SAPC, while UTP, UDP or ATP alone at 1 μM elicited a small increase in calcium concentration in mammary tumor cells. Suramin, a competitive antagonist of P2 purinoceptors, diminished the spreading of the calcium wave induced by mechanical stimulation. It also blocked the responses to SAPC, UTP, UDP and ATP. These findings suggest that the mechanical stimulation results in the release of UTP, UDP and ATP into the extracellular space which mediates induction of the spreading calcium response via P2U-type purinoceptors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374271
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  • 9
    Electronic Resource
    Electronic Resource
    Intracellular calcium responses and shape conversions induced by endothelin in cultured subepithelial fibroblasts of rat duodenal villi (1994)
    Springer
    Pflügers Archiv 428 (1994), S. 97-104 
    Details
    ISSN: 1432-2013
    Keywords: Subepithelial fibroblasts ; Rat intestine ; Intracellular calcium ; Morphological change ; Endothelin ; Substance P ; cAMP ; Fura-2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Subepithelial fibroblasts of rat duodenal villi were cultured and the physiological characteristics were studied using fura-2 fluorescence. The intracellular calcium concentration (Ca i 2+ ) responded to various substances, i.e., endothelins (ET1 and ET3), substance P, serotonin, angiotensin II, ATP, and bradykinin. The Ca i 2+ responses to ET1 (〉0.1 nM) and ET3 (〉1 nM) were transient and sometimes followed oscillations that consisted of an initial Ca2+ release from the intracellular store and a sustained Ca2+ influx. Simultaneously with Ca i 2+ measurement, changes in the cell shape were monitored using fluorescence intensity upon 360-nm excitation. Stellate cells (with thick cell body and slender processes), formed as a result of 1 mM dibutyryl(Bt2)-cAMP treatment, began to change immediately after the short-term application of the endothelin and became flat about 20 min later. This process was not affected by the depletion of extracellular Ca2+ or by the treatment with BAPTA acetoxymethyl ester that completely suppressed the Ca i 2+ response. Substance P (〉100 nM) increased Ca i 2+ , but did not induce any morphological changes. The conversion of the shape from flat to stellate, induced by Bt2cAMP treatment, was not accompanied by any Ca i 2+ change. BQ-123, a specific blocker of the ETA-type receptor, did not block either Ca i 2+ change or shape conversion at low (100 nM) concentration. The results indicated that shape conversion in subepithelial fibroblasts did not require any Ca i 2+ response. Our findings regarding the characteristics of subepithelial fibroblasts in intestinal villi imply a functional similarity to astrocytes in the brain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374846
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  • 10
    Electronic Resource
    Electronic Resource
    Release of arachidonic acid via Ca2+ increase stimulated by pyrophosphonucleotides and bradykinin in mammary tumour cells (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Cell Biochemistry and Function 13 (1995), S. 279-286 
    Details
    ISSN: 0263-6484
    Keywords: ATP ; UTP ; bradykinin ; calcium ; arachidonic acid ; mammary cell ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The relationship between the increase of intracellular Ca2+ and the release of arachidonic acid by bradykinin and pyrophosphonucleotides was studied in cultured mammary tumour cells, MMT060562. Bradykinin, ATP, UTP and UDP induced an increase of intracellular Ca2+ and the release of arachidonic acid from phospholipids into the extracellular fluid. Release of arachidonic acid was also induced by the application of the Ca2+ ionophore, A23187. Liberation of arachidonic acid by bradykinin and ATP was reduced by mepacrine, a blocker of phospholipase A2 and W-7, a calmodulin antagonist.It is suggested that the increase in cytosolic Ca2+-induced release of arachidonic acid occurs through activation of calmodulin-dependent phospholipase A2.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cbf.290130409
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