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This Article Full Text Full Text (PDF) All Versions of this Article: 538/1/79    most recent 2001.013036v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Martínez-François, J. R. Articles by Vaca, L. Search for Related Content PubMed PubMed Citation Articles by Martínez-François, J. R. Articles by Vaca, L.

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

Juan Ramón Martínez-François, Verónica Morales-Tlalpan and Luis Vaca

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 mM TEA. The current reversal potential was -86 mV (n = 12). MTX (500 pM) 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 Ca²⁺ carries I_mtx also. The resulting permeability sequence obtained with the Goldman-Hodgkin-Katz equation yielded Na⁺ (1) K⁺ (1) > Ca²⁺ (0.87). The I_mtx activation time course reflected the changes in intracellular Ca²⁺ 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 Ca²⁺ and Na⁺. Reducing the extracellular Ca²⁺ concentration below 1.8 mM prevented the activation of I_mtx and the increment in intracellular Na⁺ induced by MTX. Mn²⁺ and Mg²⁺ could not replace Ca²⁺, but Ba²⁺ could replace Ca²⁺. MTX activation of current in 10 mM Ba²⁺ was approximately 50 % of that induced in the presence of 1.8 mM Ca²⁺. When 5 mM of the Ca²⁺ 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 Ca²⁺ is also required for the activation of I_mtx. Intracellular Ba²⁺ can replace Ca²⁺ as an activator of I_mtx. However, in the presence of 10 mM Ba²⁺ the activation by MTX of the current was 50 % less than the activation with nM concentrations of free intracellular Ca²⁺.

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