Low threshold T-type calcium current in rat embryonic chromaffin cells

Area of Science:

• Neuroscience
• Cell Biology
• Biophysics

Background:

• Chromaffin cells are crucial for catecholamine secretion.
• Understanding calcium channel function is key to neuroendocrine secretion.
• Embryonic chromaffin cells exhibit distinct calcium current properties.

Purpose of the Study:

• To investigate the gating kinetics and function of low threshold T-type calcium current in developing rat chromaffin cells.
• To determine the role of T-type current in exocytosis.
• To characterize different types of calcium currents in embryonic chromaffin cells.

Main Methods:

• Patch clamp technique to record calcium currents.
• Immunohistochemistry using antibodies against dopamine beta-hydroxylase (DBH) and syntaxin.
• Measurement of membrane capacitance and amperometry to monitor exocytosis.
• Pharmacological blockade of T-type current with mibefradil and Ni(2+).

Main Results:

• Three types of chromaffin cells were identified based on calcium current properties: Type I (T-type only, 44%), Type II (HVA only, 46%), and Type III (both, 10%).
• T-type current in Type I cells activated at -50 mV, peaked at -10 mV, and did not induce exocytosis.
• High voltage-activated (HVA) calcium current induced catecholamine secretion via exocytosis in Type II and Type III cells.

Conclusions:

• Low threshold T-type calcium current is present in immature, developing chromaffin cells.
• T-type current does not appear to directly mediate exocytosis in these cells.
• Functional maturation involves the replacement of T-type current by HVA calcium current, enabling regulated catecholamine release.