L-Type Calcium Channels are a Major Source of Plasmalemmel Calcium Influx for Drosophila Cardiomyocytes

L-type Ca 2+ channels (LTCCs) play a major role in shaping cardiac action potential and thus, dysregulation of these channels underlies numerous cardiac pathologies. Understanding their modulation with high fidelity relies on investigating LTCCs in their native environment with intact binding partners. Such studies would benefit from genetic manipulation of endogenous LTCCs in cardiomyocytes, which often proves cumbersome in mammalian models. Drosophila, however, offers a potential alternative as it possesses a relatively simple heart, is genetically pliable, and expresses many conserved genes. Fluorescence in situ hybridization performed in fly cardiomyocytes demonstrated an abundance of mRNA encoding Ca-a1D and Ca-a1T, which are homologous to mammalian LTCCs and T-type Ca 2+ channels, respectively. Cardiac-specific knockdown of Ca-a1D via interfering RNA completely abolished myocyte contraction, suggesting Ca-a1D represents the primary functioning Ca 2+ channel in Drosophila hearts. To accurately probe the transmembrane currents, we successfully developed a method to isolate viable single cardiomyocytes and recorded Ca 2+ currents via patch clamping. The profile of Ca 2+ currents in individual cells when Ca 2+ channels were hypomorphic or absent, or under selective LTCC blockage by nifedipine, also confirmed the predominance of Ca-a1D current across all activation voltages. T-type currents, activated at more negative voltages, were also detected. Lastly, Ca-a1D channels displayed calcium-dependent inactivation, a critical negative feedback mechanism of LTCCs, and were augmented by forskolin, an activator of the PKA pathway. In summary, the Drosophila heart possesses a conserved compendium of Ca 2+ channels with similar regulatory mechanisms, suggesting that the fly may serve as a robust and effective platform for studying the (dys)regulation of cardiac Ca 2+ channels