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First published online February 13, 2009
Journal of Experimental Biology 212, 684-692 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.026450
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Using omeprazole to link the components of the post-prandial alkaline tide in the spiny dogfish, Squalus acanthias

Chris M. Wood1,4,5,*, Aaron G. Schultz2,5, R. Stephen Munger1,5 and Patrick J. Walsh3,4,5

1 Department of Biology, McMaster University, 1280 Main St. West, Hamilton, Ontario, Canada L8S 4K1
2 School of Life and Environmental Sciences, Deakin University, Pigdons Road, Geelong, 3217, Australia
3 Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, Ontario, Canada K1N 6N5
4 Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, FL 33149, USA
5 Bamfield Marine Sciences Centre, 100 Pachena Drive, Bamfield, British Columbia, Canada V0R 1B0

* Author for correspondence (e-mail: woodcm{at}mcmaster.ca)

Accepted 9 December 2008

After a meal, dogfish exhibit a metabolic alkalosis in the bloodstream and a marked excretion of basic equivalents across the gills to the external seawater. We used the H+, K+-ATPase pump inhibitor omeprazole to determine whether these post-prandial alkaline tide events were linked to secretion of H+ (accompanied by Cl–) in the stomach. Sharks were fitted with indwelling stomach tubes for pretreatment with omeprazole (five doses of 5 mg omeprazole per kilogram over 48 h) or comparable volumes of vehicle (saline containing 2% DMSO) and for sampling of gastric chyme. Fish were then fed an involuntary meal by means of the stomach tube consisting of minced flatfish muscle (2% of body mass) suspended in saline (4% of body mass total volume). Omeprazole pre-treatment delayed the post-prandial acidification of the gastric chyme, slowed the rise in Cl– concentration of the chyme and altered the patterns of other ions, indicating inhibition of H+ and accompanying Cl– secretion. Omeprazole also greatly attenuated the rise in arterial pH and bicarbonate concentrations and reduced the net excretion of basic equivalents to the water by 56% over 48 h. Arterial blood CO2 pressure (PaCO2) and plasma ions were not substantially altered. These results indicate that elevated gastric H+ secretion (as HCl) in the digestive process is the major cause of the systemic metabolic alkalosis and the accompanying rise in base excretion across the gills that constitute the alkaline tide in the dogfish.

Key words: feeding, shark, gastric acid secretion, H+, K+-ATPase, chyme composition, metabolic alkalosis, branchial base excretion


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