부산대학교 도서관

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 ([ET.sub.1])-induced pillar cell contraction in the lamellae of the Atlantic cod (Gadus morhua). Intra-arterial injection of the specific [ET.sub.B] receptor agonist BQ-3020 induced dose-dependent increases in ventral aortic blood pressure, gill vascular resistance, and pillar cell area (indicating contraction). The specific [ET.sub.A] 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 [ET.sub.B] receptor-like immunoreactivity (IR) associated with pillar cells in the lamellar region and in neuroendocrine cells. [ET.sub.B] receptor-like IR was also found lining the muscle layer of lamellar arterioles and filament arteries. In contrast, strong [ET.sub.A] 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 [ET.sub.B]-like receptor mediates pillar cell contraction in fishes, whereas [ET.sub.A]-like receptors may serve another function in the gill, inasmuch as [ET.sub.A] receptor-like IR is found on branchial nerves. gill; pillar cell; nerve; BQ-3020; BQ-610