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1 Department of Molecular Biosciences, University of Oslo, Oslo, Norway
2 Department of Zoophysiology, Goteborg University, Goteborg, Sweden
* To whom correspondence should be addressed. E-mail: k.o.stenslokken{at}imbv.uio.no.
By observing gill blood flow using epi-illuminating microscopy, in parallel with cardiovascular recordings and immunohistochemistry, we have tried to identify the receptor mediating endothelin 1 (ET-1) induced pillar cell contraction in the lamellae of the Atlantic cod (Gadus morhua). Intra arterial injection of the specific ETB- receptor agonist BQ-3020 induced dose dependent increases in ventral aortic blood pressure, gill vascular resistance and pillar cell area (indicating contraction). The specific ETA antagonist BQ-610 did not prevent either pillar cell contraction or increased gill vascular resistance, induced by ET-1 injection. The cardiovascular responses were corroborated by the detection of ETB receptor-like immunoreactivity (IR) associated with pillar cells in the lamellar region and in neuroendocrine cells. ETB receptor-like IR was also found lining the muscle layer of lamellar arterioles and filament arteries. In contrast, strong ETA receptor-like IR was located on branchial nerves throughout the filaments. In addition, ET-like IR was concentrated to neuroendocrine cells in the filament and lamellae. We also present data suggesting that ET mediated pillar cell contraction is widespread among teleost fish, including Atlantic cod, rainbow trout (Oncorhynchus mykiss), sculpin (Myoxocephalus scorpius) and mackerel (Scomber scombrus). Taken together our results suggest that an ETB-like receptor mediates pillar cell contraction in fishes, while ETA-like receptors may serve another function in the gill as ETA-like immunoreactivity is found on branchial nerves.
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