HYNDMAN, K/A*; EVANS, D/H; University of Florida, Gainesville; University of Florida, Gainesville: Endothelin receptors in the killifish, Fundulus heteroclitus, gill

The endothelin (ET) signaling cascade is traditionally viewed as three paracrines, ET-1, ET-2 and ET-3 that bind to two membrane bound receptors, ETA and ETB. Generally, when ETs bind to receptors on vascular smooth muscle (VSM) cells constriction is observed; however if ET binds to endothelial ETB receptors, nitric oxide (NO) and prostaglandins (PGs) are produced leading to subsequent relaxation of the underlying VSM. ET stimulation of NO and PGs can also result in inhibition of ion transport in the mammalian kidney and recently this cascade was hypothesized to inhibit ion transport in the opercular epithelial lining from the fish Fundulus heteroclitus (killifish), which is a model for the seawater teleost gill. Previous physiological experiments suggest that ET receptors (ETRs) are present in the fish gill. The gill is a multifunctional organ that receives 100% of cardiac output, which is channeled through a complex network of vessels and sinuses. We hypothesize that the ET signaling cascade may be involved in regulation of local blood pressure and flow through the gill and/or regulation of gill function. To further characterize the gill ET signaling axis, we have sequenced the mRNA of the ETRs from the killifish gill, and found three ETR transcripts from separate genes, ETA, ETB1, and ETB2. Tissue distribution and effects of environmental salinity on the killifish ETR mRNA expression were determined. Also, the cells in the gill that express ETR mRNA and proteins were localized with in situ hybridization and immunohistochemistry. Future experiments to sequence and characterize the ET genes are in progress and are needed to better understand the ET signaling cascade and its potential regulation of blood flow and gill function in fishes.