Electrophysiological characterization and functional study on sleep regulation of T-type calcium channel in Drosophila melanogaster

Abstract

Mammalian T-type $Ca^{2+}$ channels are encoded by three separate genes ($Ca_v$ 3.1, 3.2, 3.3). In mammals, T-type channels are reported to be sleep stabilizers that are important in the generation of the delta rhythms of deep sleep, but controversy remains. Progress in identifying the precise physiological functions of the T-type channels has been hindered by many factors, including possible compensation between the products of these three genes and a lack of specific pharmacological inhibitors. Invertebrates have only one T-type channel gene and its physiological functions are less well-studied. In this study $Ca-\alpha 1T$, the only $Ca_v3$ channel gene in the \emph{Drosophila melanogaster} genome, was cloned and expressed in \emph{Xenopus} oocytes or HEK-293 cells, and verified whether it is capable of passing typical T-type currents. Voltage-clamp analysis revealed that the biophysical properties of $Ca-\alpha 1T$ show mixed similarity to three mammalian T-type channels. It was also found that $Ca-\alpha 1T$ is broadly expressed across the adult fly brain in a pattern vaguely reminiscent of mammalian T-type channels. In addition, flies lacking $Ca-\alpha 1T$ show an abnormal increase in sleep duration that is most pronounced during subjective day under continuous dark conditions despite normal oscillations of the circadian clock. This study suggests invertebrate T-type $Ca^{2+}$ channels promote wakefulness rather than stabilizing sleep.