Divalent cations as charge carriers during two functionally different membrane currents in the ciliate Stylonychia

Area of Science:

• Cellular electrophysiology
• Ion channel biophysics
• Ciliate biology

Background:

• Mechanical stimulation and membrane depolarization activate ion channels in ciliates.
• Calcium (Ca2+) ions are known charge carriers in these channels.
• Understanding ion selectivity is crucial for characterizing channel function.

Purpose of the Study:

• To investigate the role of various divalent cations as charge carriers in ciliate membrane channels.
• To differentiate the ion selectivity properties of mechano-sensitive and voltage-sensitive channels.

Main Methods:

• Electrophysiological recordings in ciliates.
• Application of different divalent cations (Ca2+, Ba2+, Sr2+, Mg2+, Mn2+) to activate membrane currents.
• Analysis of ion substitution effects on mechanically and voltage-gated currents.

Main Results:

• Barium (Ba2+) and Strontium (Sr2+) ions effectively carried current through both channel types, similar to Ca2+.
• Magnesium (Mg2+) ions carried current through mechano-sensitive channels but not voltage-sensitive channels.
• Manganese (Mn2+) ions did not carry current and inhibited Ca2+ currents, suggesting channel blockage.

Conclusions:

• Mechano-sensitive and voltage-sensitive channels in ciliates exhibit differential selectivity for divalent cations.
• The distinct ion permeability profiles suggest unique structural or functional differences between these channel types.