Purely diffusive O2 transport typically is insufficient to sustain aerobic metabolism in most multicellular organisms. In small animals, however, a high surface-to-volume ratio may allow passive diffusion alone to supply sufficient O2 transfer. The purpose of this thesis was to explore the impacts of internal convection on the exchange of respiratory gases in a small complex organism, the larval zebrafish (Danio rerio). Thus, I tested the hypothesis that internal convection is required for the normal transfer of the respiratory gases O2 and CO2 and maintenance of resting aerobic metabolic rate. Use of morpholino knockdown of the VEGF-A and TNNT2 proteins allowed examination of two independent models lacking internal convection. Using micro-respirometry, I demonstrated that loss of internal convection reduces resting rates of O2 consumption and CO2 excretion in larvae at 4 days post fertilization. I also used the scanning micro-optrode technique to demonstrate that acute loss of internal convection resulted in reduced rates of cutaneous O2 flux, a trait that was reversed upon the restoration of internal convection. Finally, I demonstrated that in larval zebrafish, loss of internal convection resulted in decreased hypoxic performance and loss or severe reduction of the hypoxic cardiorespiratory responses. The results from these experiments showed that internal convection is i) required to maintain resting rates of respiratory gas transfer in the larval zebrafish, ii) important in facilitating the hypoxic cardiorespiratory responses in larval zebrafish and iii) augments O2 extraction capacity in the face of progressive hypoxia.

We identified a unique family with autosomal dominant heart disease variably expressed as restrictive cardiomyopathy (RCM), hypertrophic cardiomyopathy (HCM), and dilated cardiomyopathy (DCM), and sought to identify the molecular defect that triggered divergent remodeling pathways. Polymorphic DNA markers for nine sarcomeric genes for DCM and/ or HCM were tested for segregation with disease. Linkage to eight genes was excluded, but a cardiac troponin T (TNNT2) marker cosegregated with the disease phenotype. Sequencing of TNNT2 identified a heterozygous missense mutation resulting in an I79N substitution, inherited by all nine affected family members but by none of the six unaffected relatives. Mutation carriers were diagnosed with RCM (n = 2), non-obstructive HCM (n = 3), DCM (n = 2), mixed cardiomyopathy (n = 1), and mild concentric left ventricular hypertrophy (n = 1). Endomyocardial biopsy in the proband revealed non-specific fibrosis, myocyte hypertrophy, and no myofibrillar disarray. Restrictive Doppler filling patterns, atrial enlargement, and pulmonary hypertension were observed among family members regardless of cardiomyopathy subtype. Mutation of a sarcomeric protein gene can cause RCM, HCM, and DCM within the same family, underscoring the necessity of comprehensive morphological and physiological cardiac assessment in familial cardiomyopathy screening.