title: The role of an ancestral hyperpolarization-activated cyclic nucleotide-gated K+ channel in branchial acid-base regulation in the green crab, Carcinus maenas.
abstract: Numerous electrophysiological studies on branchial K(+) transport in brachyuran crabs have established an important role for potassium channels in osmoregulatory ion uptake and ammonia excretion in the gill epithelium of decapod crustaceans. However, hardly anything is known of the actual nature of these channels in crustaceans. In the present study, the identification of a hyperpolarization-activated cyclic nucleotide-gated potassium channel (HCN) in the transcriptome of the green crab Carcinus maenas and subsequent performance of quantitative real-time PCR revealed the ubiquitous expression of this channel in this species. Even though mRNA expression levels in the cerebral ganglion were found to be approximately 10 times higher compared with all other tissues, posterior gills still expressed significant levels of HCN, indicating an important role for this transporter in branchial ion regulation. The relatively unspecific K(+)-channel inhibitor Ba(2+), as well as the HCN-specific blocker ZD7288, as applied in gill perfusion experiments and electrophysiological studies employing the split gill lamellae revealed the presence of at least two different K(+)/NH4(+)-transporting structures in the branchial epithelium of C. maenas. Furthermore, HCN mRNA levels in posterior gill 7 decreased significantly in response to the respiratory or metabolic acidosis that was induced by acclimation of green crabs to high environmental PCO2 and ammonia, respectively. Consequently, the present study provides first evidence that HCN-promoted NH4(+) epithelial transport is involved in both branchial acid-base and ammonia regulation in an invertebrate.
authors.affiliation: Department of Zoology, University of British Columbia, 6720 University Blvd, Vancouver, British Columbia, Canada V6T 1Z4 Department of Biological Sciences, University of Manitoba, 190 Dysart Road, Winnipeg, Manitoba, Canada R3T 2N2 Fehsenfeld@zoology.ubc.ca.
authors.forename: Sandra
authors.initials: S
authors.lastname: Fehsenfeld
authors.affiliation: Department of Biological Sciences, University of Manitoba, 190 Dysart Road, Winnipeg, Manitoba, Canada R3T 2N2.
authors.forename: Dirk
authors.initials: D
authors.lastname: Weihrauch
mesh_terms: D000064:Acclimatization; D000136:Acid-Base Equilibrium; D000641:Ammonia / Q000494:pharmacology; D000818:Animals; D003386:Brachyura / Q000235:genetics / Q000378:metabolism*; D002245:Carbon Dioxide / Q000494:pharmacology; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000378:metabolism*; D015870:Gene Expression; D005880:Gills / Q000378:metabolism; D008297:Male; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism*; D000068357:Saline Waters / Q000737:chemistry; D059467:Transcriptome
chemical_list: D054815:Cyclic Nucleotide-Gated Cation Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D002245:Carbon Dioxide; D000641:Ammonia
keywords: Ammonia; Gill perfusion; HCN; HEA; Hypercapnia