Calcium channels in higher-level brain function
- Center for Neuroscience, University of California, Davis, CA 95616
Nature has a habit of using relatively simple cellular mechanisms in the service of the higher-level integrative functions of multicellular organ systems. In the article by Llinás et al. (1), published in a recent issue of PNAS, we can see an example of how a mechanism that probably evolved for maintaining the integrity of the excitable membranes of nerve, heart, glandular, and muscle cells, when placed in the context of a highly interconnected network of neurons, is recruited as a fundamental component of brain mechanisms that underlie states of consciousness and that are also involved in those of perception and cognition.
Voltage-Gated Calcium Channels
The focus of the article by Llinás et al. (1) is on the P/Q type of calcium channel, a member of a family of voltage-gated calcium channels that is itself part of an even larger superfamily of transmembrane ion channels that also includes voltage-gated sodium and potassium channels. Each calcium channel is made up of four or five protein subunits encoded by different genes (2). The large α1 subunit, like similar subunits in other voltage-gated ion channels, consists of four homologous domains, each containing six transmembrane segments. This large protein forms the conduction pore, and different segments serve as the voltage sensor and determine ion selectivity and channel conductance. Differences in the α1 subunit, which depend on the expression of at least 10 known genes, determine the properties of individual channel types. Other subunits form the links to downstream intracellular processes, modulate the pharmacological properties of the ion channel, and provide an additional basis for the diversity of channel types.
P/Q channels (formally named Cav2.1 channels) belong to the Cav2 superfamily of voltage-gated calcium channels and are distinguished from other voltage-gated calcium channels by the presence of an α1A subunit. As we see in …
*E-mail: ejones{at}ucdavis.edu
