Mn ions pass through calcium channels. A possible explanation

Area of Science:

• Neuroscience
• Cell Biology
• Biophysics

Background:

• Calcium channels are crucial for cellular electrical activity.
• The movement of ions through channels is influenced by their hydration energy.
• Understanding ion selectivity in channels provides insight into cellular function.

Purpose of the Study:

• To test the hypothesis that manganese (Mn) ions traverse calcium (Ca) channels due to their low hydration energy.
• To investigate the effects of divalent transition-metal cations (Fe, Co, Ni) on Ca and Mn spikes in myoepithelial cells.
• To determine the order of effectiveness of Fe, Co, and Ni in blocking these ionic currents.

Main Methods:

• Electrophysiological recordings of Ca and Mn spikes from Syllis spongiphila myoepithelial cells.
• Application of varying concentrations of iron (Fe), cobalt (Co), and nickel (Ni) ions to the cell bath.
• Analysis of spike parameters including abolition, rate of rise, overshoot amplitude, and current intensity required for initiation.

Main Results:

• Fe, Co, and Ni ions reversibly abolished Ca spikes in the order Ni < Fe = Co.
• These cations diminished Mn spikes by reducing the maximum rate of rise and overshoot amplitude, with effectiveness order Fe = Co < Ni.
• Increased current intensity was required for Ca and Mn spike initiation in the presence of Fe, Co, and Ni.
• At sub-blocking concentrations, Fe, Co, and Ni altered Mn and Ca spike durations.

Conclusions:

• The observed order of effectiveness of Fe, Co, and Ni in blocking Ca and Mn spikes supports the hypothesis that Mn ions pass through Ca channels by shedding hydration waters.
• The hydration energy of transition-metal cations correlates with their ability to permeate or block calcium channels.
• These findings contribute to the understanding of ion selectivity mechanisms in biological ion channels.