The Gating and Conductance Properties of CaV3.2 Low-Voltage-Activated T-Type Calcium Channels.

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  • Gating and Conductance Properties of Cav3 2 Low Voltage Activated T Type Calcium Channels

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Calcium channels are essential for excitation-contraction coupling and pacemaker potentials in cardiac muscle cells. Whereas L-type Ca2+ channels have been extensively studied, T-type channels have been poorly characterized in cardiac myocytes. We describe here the functional properties of recombinant CaV3.2 T-type Ca2+ channels expressed in mammalian cell lines. The T-type Ca2+ 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 Ca2+. Barium (Ba2+) and strontium (Sr2+) permeate the channel with similar activation kinetics. On the other hand, monovalent cations, Li+ and Na+, permeate the T-type Ca2+ channel more easily than the L-type Ca2+ channel. The permeability order of the CaV3.2 T-type Ca2+ channel among monovalent and divalent cations was determined as Ba2+>Mn2+>Ca2+>Sr2+>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 Sr2+>Ba2+>Ca2+>Li+1>Mn2+>Na+ with the conductance ratio of 1.39:1.21:1.00:0.40:0.23:0.11. The permeation profile of manganese (Mn2+) is complex. Mn2+ permeates the Ca2+ channel with a permeability similar to Ca2+ or Ba2+, but with a much smaller current density, resulting in a much smaller conductance. The properties relating to progression and recovery from inactivation in the CaV3.2 channel are substantially identical with either Ca2+ or Ba2+ as the charge carrier.<br>

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