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  • [Ca2+] i  (2)
  • pancreatic acinar cells  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Electrogenic properties of the sodium-alanine cotransporter in pancreatic acinar cells: I. Tight-seal whole-cell recordings (1986)
    Springer
    The journal of membrane biology 94 (1986), S. 99-115 
    Details
    ISSN: 1432-1424
    Keywords: cotransport ; electrogenic transport ; sodium-coupled amino-acid transport ; pancreatic acinar cells ; whole-cell recording
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Electrical currents associated with sodium-coupled alanine transport in mouse pancreatic acinar cells were studied using the method of whole-cell recording with patch pipettes. Single cells or small clusters of (electrically coupled) cells were isolated by collagenase treatment. The composition of the intracellular solution could be controlled by internal perfusion of the patch pipette. In this way both inward and outward currents could be measured under “zero-trans” conditions, i.e., with finite concentrations of sodium andl-alanine on one side and zero concentrations on the other. Inward andoutward currents for equal but opposite concentration gradients were found to be of similar magnitude, meaning that the cotransporter is functionally nearly symmetric. The dependence of current on the concentrations of sodium andl-alanine exhibited a Michaelis-Menten behavior. From the sodium-concentration dependence of current as well as from the reversal potential of the current in the presence of an alanine-concentration, gradient, a sodium/alanine stoichiometric ratio of 1:1 can be inferred. The finding that N-methylated amino acids may substitute, forl-alanine, as well as the observed pH dependence of currents indicate that the pancreatic alanine transport system is similar to (or identical with) the “A-system” which is widespread in animal cells. The transport system is tightly coupled with respect to Na+; alanine-coupled inward flow of Na+ is at least 30 times higher than uncoupled Na+ flow mediated by the cotransporter. The current-voltage characteristic of the cotransporter could be (approximately) determined from the difference of transmembrane current in the presence and in the absence ofl-alanine. The sodium-concentration dependence of the current-voltage characteristic indicates that a Na+ ion approaching the binding site from the extracellular medium has to cross part of the transmembrane electric field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871191
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  • 2
    Electronic Resource
    Electronic Resource
    Single calcium-dependent cation channels in mouse pancreatic acinar cells (1984)
    Springer
    The journal of membrane biology 81 (1984), S. 83-87 
    Details
    ISSN: 1432-1424
    Keywords: pancreatic acinar cells ; nonselective cation channel ; Ca2+-sensitivity ; patch clamp ; single-channel recording
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The Ca2+-activated nonselective cation channel in mouse pancreatic acini has been studied with the help of patch-clamp single-channel current recording in both the cell-attached conformation and in excised inside-out membrane patches. In intact resting mouse pancreatic acinar cells no unitary activity was observed. Adding saponin to the bath solution to disrupt the plasma membrane (apart from the isolated patch membrane from which current recording was made) evoked unitary inward current steps when the free ionized Ca2+ concentration in the bath ([Ca2+] i ) was 5×10−8 m or above. When an electrically isolated patch membrane was excised and the internal aspects of the plasma membrane were exposed to the bath solution, channel activation could be obtained when [Ca2+] i was 10−7 m or above. However, with the passage of time the total inward current declined and about 1 min after excision no unitary current steps could be observed. At this stage Ca2+ in micromolar concentration was needed to open the channels and several hundred micromoles of Ca2+ per liter were required for maximal channel activation. Our results indicate that the Ca2+-activated nonselective cation channel is more sensitive to internal Ca2+ than hitherto understood and that it may therefore play a role under physiological conditions in intact cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868812
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  • 3
    Electronic Resource
    Electronic Resource
    Stimulant-evoked depolarization and increase in [Ca2+] i in insulin-secreting cells is dependent on external Na+ (1990)
    Springer
    The journal of membrane biology 113 (1990), S. 131-138 
    Details
    ISSN: 1432-1424
    Keywords: patch clamp ; [Ca2+] i ; Na+ dependency ; RINm5F cell ; fura-2 ; whole cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The patch-clamp technique and measurements of single cell [Ca2+] i have been used to investigate the importance of extracellular Na+ for carbohydrate-induced stimulation of RINm5F insulin-secreting cells. Using patch-clamp whole-cell (current-clamp) recordings the average cellular transmembrane potential was estimated to be −60±1 mV (n=83) and the average basal [Ca2+] i 102±6nm (n=37). When challenged with either glucose (2.5–10mm) ord-glyceraldehyde (10mm) the cells depolarized, which led to the initiation of Ca2+ spike potentials and a sharp rise in [Ca2+] i . Similar effects were also observed with the sulphonylurea compound tolbutamide (0.01–0.1mm). Both the generation of the spike potentials and the increase in [Ca2+] i were abolished when Ca2+ was removed from the bathing media. When all external Na+ was replaced with N-methyl-d-glucamine, in the continued presence of either glucose,d-glyceraldehyde or tolbutamide, a membrane repolarization resulted, which terminated Ca2+ spike potentials and attenuated the rise in [Ca2+] i . Tetrodotoxin (TTX) (1–2 μm) was also found to both repolarize the membrane and abolish secretagogue-induced rises in [Ca2+] i .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01872887
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  • 4
    Electronic Resource
    Electronic Resource
    Comparative study of the effects of cromakalim (BRL 34915) and diazoxide on membrane potential, [Ca2+] i and ATP-sensitive potassium currents in insulin-secreting cells (1990)
    Springer
    The journal of membrane biology 114 (1990), S. 53-60 
    Details
    ISSN: 1432-1424
    Keywords: patch-clamp ; fura-2 ; KATP channels ; [Ca2+] i ; insulin-secreting cell ; RINm5F cell ; diazoxide ; cromakalim (BRL 34915) ; tolbutamide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Patch-clamp and single cell [Ca2+] i measurements have been used to investigate the effects of the potassium channel modulators cromakalim, diazoxide and tolbutamide on the insulin-secreting cell line RINm5F. In intact cells, with an average cellular transmembrane potential of −62±2 mV (n=42) and an average basal [Ca2+] i of 102±6nm (n=37), glucose (2.5–10mm): (i) depolarized the membrane, through a decrease in the outward KATP current, (ii) evoked Ca2+ spike potentials, and (iii) caused a sharp rise in [Ca2+] i . In the continued presence of glucose both cromakalim (100–200 μm) and diazoxide (100 μm) repolarized the membrane, terminated Ca2+ spike potentials and attenuated the secretagogue-induced rise in [Ca2+] i . In whole cells (voltage-clamp records) and excised outside-out membrane patches, both cromakalim and diazoxide enhanced the current by opening ATP-sensitive K+ channels. Diazoxide was consistently found to be more potent than cromakalim. Tolbutamide, a specific inhibitor of ATP-sensitive K+ channels, reversed the effects of cromakalim on membrane potential and KATP currents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869384
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