Voltage‐sensitive Ca2+ channels (VSCCs) are often heteromultimeric complexes. The VSCC subtype specifically expressed by skeletal muscle has long been known to contain a γ subunit, γ1, that is only expressed in this tissue. Recent work, initiated by the identification of the mutation present in the stargazer mouse, has led to the identification of a series of novel potential Ca2+ channel γ subunits expressed in the CNS. Based on bioinformatic techniques we identified and cloned the human γ2, γ3 and γ4 subunits. TaqMan analysis was used to quantitatively characterise the mRNA expression patterns of all the γ subunits. All three subunits were extensively expressed in adult brain with overlapping but subunit‐specific distributions. γ2 and γ3 were almost entirely restricted to the brain, but γ4 expression was seen in a broad range of peripheral tissues. Using a myc epitope the γ2 subunit was tagged both intracellularly at the C‐terminus and on a predicted extracellular site between the first and second transmembrane domains. The cellular distribution was then examined immunocytochemically, which indicated that a substantial proportion of the cellular pool of the γ2 subunit was present on the plasma membrane and provided initial evidence for the predicted transmembrane topology of the γ subunits. Using co‐transfection techniques we investigated the functional effects of each of the γ subunits on the biophysics of the T‐type VSCC encoded by the α1I subunit. This revealed a substantially slowed rate of deactivation in the presence of γ2. In contrast, there was no significant corresponding effect of either γ3 or γ4 on α1I subunit‐mediated currents.

Chlorpromazine is a neuroleptic antipsychotic agent with a long history of clinical use. Its primary mode of action is thought to be through modulation of monoaminergic inter-neuronal communication; however, its side-effect profile indicates substantial activities in other systems. Recent work has begun to uncover actions of this compound on ion channels. In this light we have investigated the actions of chlorpromazine on the recombinant alpha1E subunit-encoded voltage-sensitive Ca2+ channel (VSCC) that is believed to encode drug-resistant R-type currents found in neurones and other cells. Chlorpromazine produced a dose-dependent antagonism of these channels that was reversed on drug removal. The mean IC50 was close to 10 microM. At this concentration, the level of antagonism observed was dependent on the membrane potential, with greater inhibition being observed at more negative test potentials. Furthermore, chlorpromazine induced substantial changes in the steady-state inactivation properties of alpha1Ebeta3-mediated currents, although it was not seen to elicit a corresponding change in inactivation kinetics. These results are discussed with regard to the possible clinical mechanisms of chlorpromazine actions.