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Modulation of a calcium-activated chloride current by Maitotoxin
M Martínez1, C Salvador, J M Farias
1Departamento de Fisología, Instituto Nacional de Cardiología, Mexico D.F., Mexico.
Abstract:
The effect of Maitotoxin (MTX) on the calcium-activated chloride current (ICl-Ca) from Xenopus oocytes was studied, applying the two-electrode voltage clamp technique. MTX increased the current amplitude at all the voltages explored and reduced the time to reach the maximum current level (time to peak). At low toxin concentrations (15 pM), both effects were fully reversible. Activation of ICl-Ca by MTX was secondary to the increment in the intracellular Ca2+ concentration induced by this toxin, since incubation of the oocytes with the cell-permeant Ca2+ chelator BAPTA-AM, greatly reduced the effect of MTX on ICl-Ca. Furthermore, external chloride ions removal also diminished the MTX effect on the current, strongly suggesting that the main current activated by MTX is ICl-Ca. Subsequent applications of a fixed toxin concentration after toxin washout resulted in enhanced ICl-Ca, suggesting that the toxin effect potentiates.
Insights
Maitotoxin (MTX) activates calcium-activated chloride currents (ICl-Ca) in Xenopus oocytes by increasing intracellular calcium. This effect is reversible at low concentrations and potentiates with repeated exposure.
Area of Science:
- Marine natural products
- Ion channel physiology
- Oocyte electrophysiology
Background:
- Maitotoxin (MTX) is a potent marine toxin.
- Calcium-activated chloride currents (ICl-Ca) play crucial roles in cellular function.
- Xenopus oocytes are a widely used model system for studying ion channels.
Purpose of the Study:
- To investigate the effects of Maitotoxin (MTX) on calcium-activated chloride currents (ICl-Ca) in Xenopus oocytes.
- To elucidate the mechanism by which MTX modulates ICl-Ca.
Main Methods:
- Two-electrode voltage clamp technique was employed to measure ionic currents.
- Experiments involved varying MTX concentrations and extracellular/intracellular conditions.
- The role of intracellular calcium was assessed using the chelator BAPTA-AM.
Main Results:
- MTX significantly increased ICl-Ca amplitude and reduced the time to peak current.
- These effects were reversible at low MTX concentrations (15 pM).
- MTX-induced ICl-Ca activation was dependent on intracellular calcium levels and external chloride ions.
- Repeated MTX applications led to potentiation of the ICl-Ca response.
Conclusions:
- Maitotoxin directly activates calcium-activated chloride currents in Xenopus oocytes.
- The primary mechanism involves MTX-induced elevation of intracellular calcium.
- MTX exhibits a potentiating effect on ICl-Ca with repeated exposure, suggesting complex interactions.