Molecular Properties of Voltage-Gated Calcium Channels

Native Voltage-Gated Ca Channels Early electrophysiological recordings from neurons, muscle and endocrine cells revealed voltage-activated calcium (Ca) currents with distinct characteristics, suggesting the existence of two major classes of Ca2+ channels based upon the membrane potentials at which they first open (see chapter by Tsien); low-voltage activated (LVA) and high-voltage activated (HVA). The LVA (or T-type) channels, typically have a small conductance (8-12 pico Siemens (pS)), open in response to small changes from the resting membrane potential and inactivate rapidly. In contrast, the HVA currents generally possess larger conductances (15-25 pS), are activated by stronger depolarizations and display variable inactivation kinetics. To date, multiple types of HVA Ca2+ channels (L-, N-, P/Qand R-type) have been categorized on the basis of a number of criteria including, single channel conductance, kinetics, pharmacology, and cellular distribution.1-4