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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY
1Physiology Program, Department of Molecular Biosciences, University of Oslo, Oslo, Norway; and 2Department of Zoophysiology, Göteborg University, Göteborg, Sweden
Submitted 13 September 2004 ; accepted in final form 7 October 2005
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 (ET) type 1 (ET1)-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 receptor 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 found on branchial nerves throughout the filaments. In addition, ET-like IR was concentrated in 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, whereas ETA-like receptors may serve another function in the gill, inasmuch as ETA receptor-like IR is found on branchial nerves.
gill; pillar cell; nerve; BQ-3020; BQ-610
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