Genetic and pharmacological identification of ion channels central to the Drosophila cardiac pacemaker.

Drosophila provides an excellent model for delineating the role of ion channels in the origin and transmission of heartbeat. We report here tests in Drosophila on a wide range of mutations and pharmacological agents known to interfere with K+, Ca2+, Na+, and Cl- ion channels in well-characterized ways. We find K+ channels are central to heart function. Tetraethylammonium, which blocks all four K+ currents, slowed the heart. We were able to distinguish among these currents. The mutation slowpoke and the agent charybdotoxin, both of which affect a fast Ca(2+)-gated K+ channel, virtually eliminate heartbeat. Shaker and ether-a-go-go, which encode subunits of K+ channels, have moderate, possibly regulatory effects. "OPQ-type" Ca2+ channels are critical. omega-Conotoxin MVIIC, which blocks these channels, virtually stops the heart. Amiloride, which may affect T-type Ca2+ channels, has no effect, nor do the L-type Ca2+ blockers verapamil and diltiazem. temperature induced paralysis E, involved in the function of Na+ channels, the Na+ channel blockers tetrodotoxin and amiloride, and the Cl- blockers mefanamic and niflumic acids have no effect. Na+ and Cl- channels thus appear unnecessary for cardiac function.