Characterization of the maitotoxin-activated cationic current from human skin fibroblasts

Characterization of the maitotoxin-activated cationic current from human skin fibroblasts

The maitotoxin (MTX)-induced cationic current ( I mtx ) from human skin fibroblasts was characterized using the patch-clamp technique in whole-cell configuration. Under resting conditions (absence of MTX), the main current observed is produced by an outwardly rectifying K + channel which is inhibite...

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Bibliographic Details
Published in:The Journal of physiology Vol. 538; no. 1; pp. 79 - 86
Main Authors: Juan Ramón Martínez-François, Verónica Morales-Tlalpan, Luis Vaca
Format: Journal Article
Language:English
Published: Oxford, UK The Physiological Society 01-01-2002
Blackwell Publishing Ltd
Blackwell Science Inc
Subjects:
Barium - physiology
Calcium - physiology
Cations, Divalent - metabolism
Cells, Cultured
Electric Conductivity
Extracellular Space - metabolism
Fibroblasts - drug effects
Fibroblasts - physiology
Humans
Intracellular Membranes - metabolism
Ion Channels - physiology
Magnesium - physiology
Marine Toxins - pharmacology
Oxocins
Patch-Clamp Techniques
Potassium - physiology
Research Papers
Skin - cytology
Skin Physiological Phenomena - drug effects
Sodium - physiology
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Summary:The maitotoxin (MTX)-induced cationic current ( I mtx ) from human skin fibroblasts was characterized using the patch-clamp technique in whole-cell configuration. Under resting conditions (absence of MTX), the main current observed is produced by an outwardly rectifying K + channel which is inhibited by 1 m m TEA. The current reversal potential was −86 mV ( n = 12). MTX (500 p m ) activated a current with a linear current–voltage relationship and a reversal potential of −10 mV ( n = 10). Replacing the extracellular Na + and K + with N -methyl- d -glucamine (NMDG) caused a shift of the reversal potential to a value below −100 mV, indicating that Na + and K + , but not NMDG, carry I mtx . Further ion selectivity experiments showed that Ca 2+ carries I mtx also. The resulting permeability sequence obtained with the Goldman–Hodgkin–Katz equation yielded Na + (1) ≈ K + (1) > Ca 2+ (0.87). The I mtx activation time course reflected the changes in intracellular Ca 2+ and Na + measured with the fluorescent indicators fura-2 and SBFI, respectively, suggesting that the activation of I mtx brings about an increment in intracellular Ca 2+ and Na + . Reducing the extracellular Ca 2+ concentration below 1.8 m m prevented the activation of I mtx and the increment in intracellular Na + induced by MTX. Mn 2+ and Mg 2+ could not replace Ca 2+ , but Ba 2+ could replace Ca 2+ . MTX activation of current in 10 m m Ba 2+ was approximately 50 % of that induced in the presence of 1.8 m m Ca 2+ . When 5 m m of the Ca 2+ chelator BAPTA was included in the patch pipette, MTX either failed to activate the current or induced a small current (less than 15 % of the control), indicating that intracellular Ca 2+ is also required for the activation of I mtx . Intracellular Ba 2+ can replace Ca 2+ as an activator of I mtx . However, in the presence of 10 m m Ba 2+ the activation by MTX of the current was 50 % less than the activation with n m concentrations of free intracellular Ca 2+ .
ISSN:0022-3751
1469-7793
DOI:10.1113/jphysiol.2001.013036