Roles of the Sarcoplasmic/Endoplasmic Reticulum Ca2+-ATPase, Plasma Membrane Ca2+-ATPase and Na+/Ca2+ Exchanger in Regulation of Heart Rate in Larval Drosophila~!2010-03-10~!2010-08-13~!2010-08-27~!

Abstract

Abstract:We investigated the roles of three regulatory proteins that impact [Ca 2+ ] i within cardiac myocytes of Drosophila melanogaster. The NCX (Na + /Ca 2+ exchanger), PMCA (plasma membrane Ca 2+ -ATPase) and SERCA (sarcoplasmic/endoplasmic reticulum Ca 2+ -ATPase) were compromised by ionic, pharmacological, mutationalmanipulation, and with a combination of approaches, while heart rate (HR) was monitored. A decrease in SERCA function reduced HR more for intact larva in comparison to a dissected larva. Dissected preparations were used to expose the heart directly to agents. A compromised PMCA also reduced HR; however, attenuated NCX function by low [Na + ] o increased HR. KBR7943, a blocker of Ca 2+ entry via NCX, exposure increased HR. A combined loss of function in all three channels did not show a significant change in HR. The results indicate that NCX and PMCA are important in regulating HR, whereas SERCA does not have as pronounced role for dissected preparations. However, with intact preparations the loss of SERCA function by a mutation does have a significant impact on HR. Pharmacological approaches to alter PMCA and SERCA paralleled the results obtained by ionic and mutational approaches. To further understand the pacemaker activity, intracellular recordings were obtained. Mapping of action-potentials in myocytes revealed that the caudal region of the heart has large amplitude potentials and is likely to contain the pacemaker cells. The Drosophila heart can serve as a genetic model in understanding regulation of ionic currents for pacing cells of various types.

Pharmacological identification of cholinergic receptor subtypes on Drosophila melanogaster larval heart

“…The larval dissection is described in detail by Gu and Singh (1995) and in video by Cooper et al (2009). An illustration of the preparation used can be found in Desai-Shah et al (2010). In short, third instar larvae were opened by an incision in the ventral midline and the internal organs were washed aside by saline in order to expose the intact heart to various solutions.…”

“…Hemolymph is drawn into the heart through ostia in the posterior pump and circulated through an aorta back into the visceral lumen (Molina and Cripps 2001). The pacemaker of the larval heart is located caudally and, like in the human heart, is myogenic (Dowse et al 1995;Gu and Singh 1995;Johnson et al 1998Johnson et al , 2001Rizki 1978) meaning action potentials in this tissue are initiated in the absence of neural innervation within the cardiac muscle itself (Cooper et al 2009;Desai-Shah et al 2010). In the late 3rd instar there appear to be neurons innervating the rostral tissue of the aorta, but the function of this innervation has not been addressed (Johnstone and Cooper 2006).…”

Aging and CaMKII Alter Intracellular Ca2+ Transients and Heart Rhythm in Drosophila melanogaster

“…Moreover, it is known that Drosophila melanogaster has similar proteins responsible for Ca 2+ handling in the cardiomyocyte, [1] and that adult fruit fly heart recapitulates several aspects of Ca 2+ regulation observed in human myocardium [2].…”

Pharmacological analysis of dopamine modulation in theDrosophila melanogasterlarval heart

“…Higher [Ca 2+ ] o is known to substantially increase HR and further modulatory effects are difficult to ascertain at higher frequencies (Desai‐Shah et al. ). After washing away DA in the low calcium solution there was a 40% increase in HR.…”

“…) and a sodium/calcium exchanger (Desai‐Shah et al. ). Larval HR is positively correlated with extracellular calcium, for example, decreasing [Ca 2+ ] o from 1.0 mmol/L to 0.5 mM decreases HR by over 50%, and increasing [Ca 2+ ] o from 1.0 to 2.0 mmol/L increases HR by 40% (Desai‐Shah et al.…”