Date of Award

Fall 12-2016

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Advisor

Harold B. Dowse

Second Committee Member

Mary S. Tyler

Third Committee Member

Leonard J. Kass

Additional Committee Members

Clarissa Henry

Erik Johnson

Abstract

This dissertation studies calcium channels, exchangers, and pumps (components) in cardiac pacemaking in Drosophila melanogaster. One goal of this work was to further establish Drosophila as a model organism for heart research, while another was to identify links between sarcolemmal and sarcoplasmic reticulum (SR) oscillators, if one is dominant over the other, and/or if one oscillator can compensate for decreased function of the other. Another goal was to identify heartbeat frequency and rhythmicity phenotypes associated with decreased function in various pacemaking components. Heartbeat was examined in animals that carried genetic mutations in or decreased expression of genes that encode these components, and animals exposed to component-specific pharmacological blockers. mRNA expression was also examined. Results indicate that components with similar function may become upregulated to compensate for decreased function or complete lack of the other. Findings also suggest that in wild type strains, the sarcolemmal oscillator is dominant over that of the SR, but that both oscillators can compensate for one another.

I also examined calcium-dependent inactivation in high voltage-activated calcium channels and its necessity in pacemaking by injecting varying concentrations of barium chloride into P1 prepupae and examining its effects on heartbeat. Barium was used because of its ability to pass through calcium channels, while not efficiently binding calmodulin, essential for calcium-dependent inactivation (Ben-Johny & Yue, 2014; Chao et al., 1984). Heartbeat in prepupae that carried certain mutations appeared to be more reliant than others on calcium-dependent inactivation, meaning components that do not require calcium-dependent inactivation may compensate for a lack of functional components that do. Moreover, I found that certain mutations may cause defective physiological ion regulation, indicative of heart failure (Bers, 2014).

Chapter 4 indicates that suppressing tryptophan 2,3-dioxygenase causes a slow, rhythmic heartbeat phenotype. Tryptophan 2,3-dioxygenase activity is rate-limiting serotonin and melatonin production (Kanai et al., 2009). These mutants likely have increased serotonin production but have an opposite phenotype exhibited by animals injected with serotonin (Johnson et al., 1997). This slow heartbeat phenotype indicates that these mutants are likely less sensitive to serotonin than wild type, and that overall nervous system influence on heartbeat may be decreased.

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