High-voltage-activated calcium current in developing neurons is insensitive to nifedipine

Area of Science:

• Neuroscience
• Cardiology
• Pharmacology

Background:

• High-threshold, voltage-activated (HVA) calcium channels are crucial for cellular excitability.
• Nifedipine is a known blocker of L-type calcium channels, primarily studied in cardiac cells.
• Neuronal calcium currents have distinct properties that may differ from cardiac channels.

Purpose of the Study:

• To investigate the effect of nifedipine on HVA calcium currents in diverse neuronal and cardiac cell types.
• To differentiate the pharmacological properties of neuronal HVA currents from cardiac HVA currents.

Main Methods:

• Electrophysiological analysis of macroscopic HVA calcium currents.
• Application of nifedipine and omega-conotoxin to postnatal rat Purkinje and dorsal root ganglion (DRG) neurons, embryonic chick DRG neurons, and adult cat ventricular myocytes.
• Analysis of current inactivation kinetics and voltage-dependence.

Main Results:

• Nifedipine reduced HVA current in myocytes in a voltage-sensitive manner, consistent with L-type channel blockade.
• Neuronal HVA current analysis was complicated by slow, voltage-dependent, and irreversible inactivation.
• No evidence of a nifedipine-sensitive component was found in neuronal HVA currents after accounting for inactivation.
• Omega-conotoxin irreversibly reduced DRG neuron currents, while cardiac and Purkinje cells were unaffected.

Conclusions:

• Neuronal HVA currents (N-type and P-type) are pharmacologically distinct from cardiac HVA currents (L-type).
• The distinct biophysical properties, particularly slow inactivation, of neuronal HVA currents necessitate specific analytical approaches.
• These findings support the classification of distinct neuronal and cardiac calcium channel subtypes.