Divalent metals differentially block cloned T-type calcium channels

Area of Science:

• Pharmacology
• Neuroscience
• Ion Channel Physiology

Background:

• T-type calcium channels are crucial for neuronal function and are implicated in various physiological and pathological processes.
• Selective blockers are essential tools for dissecting the specific roles of different calcium channel subtypes.

Purpose of the Study:

• To investigate the pharmacological profiles of divalent metals (Cu2+, Pb2+, Zn2+) as blockers of cloned T-type calcium channel isoforms (alpha1G, alpha1H, alpha1I).
• To evaluate the selectivity of these metal ions for native T-type calcium channels over high voltage-activated calcium channels in rat sympathetic pelvic neurons.

Main Methods:

• Electrophysiological recordings were used to assess the blockade of cloned T-type calcium channel isoforms (alpha1G, alpha1H, alpha1I) by Cu2+, Pb2+, and Zn2+.
• The effects of these metals on native low and high voltage-activated calcium channels in rat sympathetic pelvic neurons were also evaluated.

Main Results:

• Cu2+ and Zn2+ demonstrated concentration-dependent blockade of all three T-type channel isoforms, with higher affinity for alpha1H currents (IC50 = 0.9 microM for Cu2+, 2.3 microM for Zn2+).
• In pelvic neurons, Zn2+ exhibited strong selectivity for T-type calcium currents over high voltage-activated currents.
• Pb2+ did not display distinctive selectivity in blocking calcium channels.

Conclusions:

• Cu2+ and Zn2+ can serve as selective blockers for alpha1H T-type calcium channels at low concentrations, similar to Ni2+.
• These findings provide valuable pharmacological tools for further research into the specific functions of T-type calcium channels, particularly the alpha1H isoform.