High- and low-threshold calcium currents in neurons acutely isolated from rat sensorimotor cortex

Area of Science:

• Neuroscience
• Electrophysiology
• Molecular Biology

Background:

• Neuronal function relies on calcium (Ca2+) influx.
• Different types of voltage-gated calcium channels (VGCCs) mediate these currents, but their specific roles and properties in certain neuronal populations require further elucidation.

Purpose of the Study:

• To characterize the electrophysiological properties of distinct high-threshold and low-threshold calcium currents in rat frontoparietal cortical neurons.
• To investigate the pharmacological and ionic sensitivities of these currents to differentiate underlying calcium channel types.

Main Methods:

• Neuron isolation from rat frontoparietal cortex (14-28 days old) using papain treatment and trituration.
• Whole-cell voltage clamp recordings to analyze calcium currents.
• Pharmacological manipulation using blockers (Cd2+, Ni2+, nimodipine, omega-conotoxin) and activators (Bay K 8644).
• Ionic substitution experiments (Ca2+ with Ba2+) to assess current characteristics.

Main Results:

• A slowly inactivating, high-threshold Ca2+ current activated at potentials positive to -45 mV was identified.
• A transient, low-threshold Ca2+ current activated at potentials positive to -65 mV was observed.
• Differential sensitivity to Cd2+ (high-threshold) and Ni2+ (low-threshold) was noted.
• High-threshold currents were enhanced by Bay K 8644 and reduced by nimodipine and omega-conotoxin.
• Low-threshold currents were reduced by nimodipine but unaffected by Bay K 8644 and omega-conotoxin.

Conclusions:

• The distinct biophysical and pharmacological properties strongly suggest the involvement of different voltage-gated calcium channel types underlying the observed high-threshold and low-threshold currents.
• These findings contribute to understanding neuronal excitability and the specific roles of different calcium channels in cortical function.