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Calcium-dependent potentiation of M-current in bullfrog sympathetic neurons
T Tokimasa1, T Shirasaki, M Yoshida
1Department of Physiology, Tokai University Medical School, Isehara, Japan. tokimasa@is.icc.u-tokai.ac.jp
Abstract:
Whole-cell voltage-clamp recordings were made from cultured bullfrog sympathetic neurons to measure the steady-state activation curve of M-type potassium current. When measured with a calcium-deficient (10 nM) pipette solution M-conductance was 4.8 nS at -35 mV having the 50%-activation voltage at-20 mV. Respective values were 17.2 nS at -35 mV with the 50%-activation voltage at -42 mV when measured with a calcium-rich (1 microM) solution, indicating the hyperpolarizing displacement of the activation curve with high internal calcium. It is suggested that intracellular calcium ions can modulate kinetics of M-current which thereby regulate the number of M-channels being open at given membrane potentials.
Insights
Intracellular calcium modulates M-current kinetics in bullfrog neurons. Higher internal calcium shifts the M-type potassium current activation curve, affecting channel opening at specific membrane potentials.
Area of Science:
- Neuroscience
- Electrophysiology
- Ion Channel Physiology
Background:
- M-type potassium current (IM) plays a crucial role in neuronal excitability.
- The modulation of IM by intracellular factors is critical for regulating neuronal firing patterns.
Purpose of the Study:
- To investigate the effect of intracellular calcium concentration on the steady-state activation kinetics of M-type potassium current in bullfrog sympathetic neurons.
Main Methods:
- Whole-cell voltage-clamp recordings were performed on cultured bullfrog sympathetic neurons.
- The steady-state activation curve of the M-current was measured using different internal calcium concentrations (10 nM and 1 microM).
Main Results:
- With low internal calcium (10 nM), M-conductance was 4.8 nS at -35 mV, with a 50%-activation voltage of -20 mV.
- With high internal calcium (1 microM), M-conductance increased to 17.2 nS at -35 mV, and the 50%-activation voltage shifted to -42 mV.
- This indicates a hyperpolarizing shift in the activation curve with increased intracellular calcium.
Conclusions:
- Intracellular calcium ions can modulate the kinetics of M-current.
- Calcium's modulation of M-current kinetics influences the number of M-channels open at given membrane potentials, thereby regulating neuronal excitability.