Genetic and Pharmacological Identification of Ion Channels Central to theDrosophilaCardiac Pacemaker

Abstract

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.

Calcium-activated potassium channel of the tobacco hornworm,Manduca sexta: molecular characterization and expression analysis

“…This change in pacemaker regions may occur as a result of the heart becoming innervated during the metamorphic transition Dulcis et al, 2001). Because dSlo channels are critical for pacemaker activity in Drosophila (Johnson et al, 1998), it is possible that developmental regulation of msSlo channel By contrast, transcript levels are dramatically increased in the adult thoracic DLM in comparison with larval msslo mRNA levels. These changes are temporally correlated to the switch in the contractile properties of the thoracic DLMs from tonic in larvae to phasic in adults.…”

“…The role that dSlo plays in maintaining heartbeat is critical, as both slo mutants and animals injected with the agent charybdotoxin, which blocks fast Ca 2+ -gated K + channels, exhibit greatly diminished heartbeat and rhythmicity (Johnson et al, 1998). Given the importance of the Slo channel in the Drosophila heart, it is likely that the developmental regulation of msslo expression we observed in Manduca has stage-specific physiological relevance.…”

“…In the Drosophila heart, four K + currents, including a Slo current, have been detected through mutational and pharmacological analysis (Johnson et al, 1998). The role that dSlo plays in maintaining heartbeat is critical, as both slo mutants and animals injected with the agent charybdotoxin, which blocks fast Ca 2+ -gated K + channels, exhibit greatly diminished heartbeat and rhythmicity (Johnson et al, 1998).…”

Genetic Control of Heart Function and Aging in Drosophila

“…Mutations in a number of ion channels and transporters have been found to alter larval heart rate, including in SERCA, the Sarco-endoplasmic reticulum Ca 2+ -ATPase, and in the Ca 2+ -channel encoded by cacophony (Ray andDowse 2005,Sanyal et al 2006). Moreover, vertebrate homologs of potassium channels encoded by either-a-gogo (eag) and KCNQ are responsible for repolarization of the cardiac action potential (Kr/HERG and Ks/KCNQ; for review see Sanguinetti and Tristani-Firouzi, 2006) , and eag and KCNQ mutants in Drosophila also perturb proper heart function, further underlining the remarkable functional parallels in basic cardiac physiology between flies and humans (Johnson et al 1998;Ocorr et al 2007; for review see Bodmer et al 2005). Investigation of ion channel expression, their cardiac-specific functions and detailed contractile properties of the Drosophila heart has become more readily possible in recent years, with the advent of new experimental techniques applied to this small organism.…”

Tinman/Nkx2-5 acts via miR-1 and upstream of Cdc42 to regulate heart function across species

“…In particular, we focused on ion channel genes that have previously been shown to regulate heart function in the adult fly (Bodmer, 2005;Akasaka et al, 2006;Ocorr et al, 2007;Qian et al, 2008a). Of these candidates, the two potassium channels dSUR and slowpoke were most severely down-regulated ( (Johnson et al, 1998;Akasaka et al, 2006). To determine whether Cdc42 genetically interacted with as in the fly.…”