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The gating and conductance properties of Cav3.2 low-voltage-activated T-type calcium channels
Toshihiko Kaku1, Tae-Seong Lee, Makoto Arita
1Department of Cardiovascular Science, Oita Medical University, 1-1 Idaigaoka, Hasama, Oita, 879-5593 Japan.
Abstract:
Calcium channels are essential for excitation-contraction coupling and pacemaker potentials in cardiac muscle cells. Whereas L-type Ca(2+) channels have been extensively studied, T-type channels have been poorly characterized in cardiac myocytes. We describe here the functional properties of recombinant Ca(V)3.2 T-type Ca(2+) channels expressed in mammalian cell lines. The T-type Ca(2+) current showed a rapid activation and an inactivation phase in response to depolarization, and it displayed a window current over the voltage range from -60 to -40 mV in 1 to 10 mM external Ca(2+). Barium (Ba(2+)) and strontium (Sr(2+)) permeate the channel with similar activation kinetics. On the other hand, monovalent cations, Li(+) and Na(+), permeate the T-type Ca(2+) channel more easily than the L-type Ca(2+) channel. The permeability order of the Ca(V)3.2 T-type Ca(2+) channel among monovalent and divalent cations was determined as Ba(2+)>Mn(2+)>Ca(2+)>Sr(2+)>Li(+1)>Na(+) with the permeability order of 1.39:1.25:1.00:0.95:0.55:0.29. The ionic conductance sequence for cations relative to calcium was Sr(2+)>Ba(2+)>Ca(2+)>Li(+1)>Mn(2+)>Na(+) with the conductance ratio of 1.39:1.21:1.00:0.40:0.23:0.11. The permeation profile of manganese (Mn(2+)) is complex. Mn(2+) permeates the Ca(2+) channel with a permeability similar to Ca(2+) or Ba(2+), but with a much smaller current density, resulting in a much smaller conductance. The properties relating to progression and recovery from inactivation in the Ca(V)3.2 channel are substantially identical with either Ca(2+) or Ba(2+) as the charge carrier.
Insights
This study characterizes recombinant Ca(V)3.2 T-type calcium channels, revealing their unique ion permeability and conductance properties. Understanding these cardiac calcium channels is crucial for cardiac function research.
Area of Science:
- Cardiovascular Physiology
- Molecular Cardiology
- Ion Channel Biophysics
Background:
- T-type calcium channels are crucial for cardiac excitation-contraction coupling and pacemaker potentials.
- While L-type calcium channels are well-studied, cardiac T-type channels remain less characterized.
- This research focuses on the functional properties of recombinant Ca(V)3.2 T-type calcium channels.
Purpose of the Study:
- To functionally characterize recombinant Ca(V)3.2 T-type calcium channels expressed in mammalian cell lines.
- To determine the ion permeability and conductance properties of these channels for various cations.
- To compare the properties of T-type channels with those of L-type channels.
Main Methods:
- Expression of recombinant Ca(V)3.2 T-type calcium channels in mammalian cell lines.
- Electrophysiological recordings to analyze channel activation, inactivation, and window currents.
- Measurement of ion permeability and conductance using different cations (Ca(2+), Ba(2+), Sr(2+), Li(+), Na(+), Mn(2+)).
Main Results:
- Ca(V)3.2 channels exhibit rapid activation and inactivation, with a window current between -60 and -40 mV.
- Barium (Ba(2+)) and strontium (Sr(2+)) permeate the channel similarly to calcium (Ca(2+)).
- Monovalent cations (Li(+), Na(+)) show higher permeability through T-type channels compared to L-type channels.
- Permeability order: Ba(2+)>Mn(2+)>Ca(2+)>Sr(2+)>Li(+)>Na(+). Conductance order: Sr(2+)>Ba(2+)>Ca(2+)>Li(+)>Mn(2+)>Na(+).
- Manganese (Mn(2+)) permeation is complex, with similar permeability to Ca(2+) but lower conductance.
- Inactivation kinetics are similar for Ca(2+) and Ba(2+) charge carriers.
Conclusions:
- Recombinant Ca(V)3.2 T-type calcium channels possess distinct functional properties.
- The differential ion permeability and conductance offer insights into their role in cardiac electrophysiology.
- Further characterization of these channels can advance understanding of cardiac function and disease.
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