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Omega-conotoxin binding and effects on calcium channel function in human neuroblastoma and rat pheochromocytoma cell

E Sher1, A Pandiella, F Clementi

  • 1Dept of Medical Pharmacology, University of Milan, Italy.

FEBS Letters
|August 1, 1988
PubMed

Insights

Omega-conotoxin specifically binds to certain voltage-operated calcium channels (VOCCs) in neuroblastoma and pheochromocytoma cells. This peptide toxin primarily blocks the initial calcium influx phase, suggesting a unique VOCC subtype interaction.

Area of Science:

  • Neuroscience
  • Pharmacology
  • Cell Biology

Background:

  • Voltage-operated calcium channels (VOCCs) are crucial for neuronal function.
  • Omega-conotoxin is a specific peptide toxin targeting certain VOCC subtypes.
  • IMR32 neuroblastoma and PC12 pheochromocytoma cells are relevant models for studying neuronal ion channels.

Purpose of the Study:

  • To investigate the binding characteristics of omega-conotoxin in IMR32 and PC12 cell lines.
  • To determine the specific VOCC subtypes targeted by omega-conotoxin.
  • To elucidate the functional effects of omega-conotoxin on depolarization-induced calcium influx.

Main Methods:

  • Radioligand binding assays using omega-conotoxin.
  • Fura-2 fluorimetric technique to measure intracellular calcium ([Ca2+]i) rise.
  • Cellular depolarization using high potassium (K+) concentrations.
  • Antagonism studies with dihydropyridines, verapamil, and CaCl2.

Main Results:

  • Omega-conotoxin exhibited specific, saturable, high-affinity binding in both cell lines.
  • Toxin binding was antagonized by high CaCl2 concentrations but not by dihydropyridines or verapamil.
  • Depolarization-induced [Ca2+]i rise showed an initial peak and a prolonged plateau.
  • Omega-conotoxin predominantly blocked the initial calcium influx peak.
  • Nitrendipine, a dihydropyridine, primarily affected the plateau phase of calcium influx.

Conclusions:

  • Omega-conotoxin targets a distinct subgroup of VOCCs in IMR32 and PC12 cells.
  • This VOCC subgroup is resistant to dihydropyridine blockade.
  • The findings suggest differential roles for VOCC subtypes in calcium signaling.

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