Characterization of ion transport in the isolated epipodite of the lobster Homarus americanus.
Unfolded epipodite isolated from American lobsters (Homarus americanus) acclimated to dilute seawater was mounted in an Ussing-type chamber for ion transport studies. The split epipodite is an electrically polarized, one-cell-layer epithelium supported with cuticle. Under open-circuit conditions, the transepithelial potential was -4.2+/-1.0 mV (N=38). In the short-circuited epithelium, the current averaged over all of the preparations was -185.4+/-20.2 A cm(-2) (N=38) with a high conductance of 55.2+/-11.4 mS cm(-2) (N=38), typical for a leaky epithelium. The Na:Cl absorptive flux ratio was 1:1.6; ion substitution experiments indicated that the transport of Na+ and Cl- is coupled. Basolateral application of the Cl- channel blockers 5-nitro-2-(3-phenylpropylamino) benzoate (NPPB) and niflumic acid (NFA) dose-dependently inhibited short-circuit current (ISC). Secretory K+ (Rb+) fluxes exceeded influxes and were inhibited by the Na+/K+-ATPase inhibitor ouabain and the K+ channel blocker cesium. Western blot analysis showed that Na+/K+-ATPase alpha-subunit protein was more highly expressed in the epipodite of lobsters acclimated to 20 p.p.t. compared with animals acclimated to seawater (34 p.p.t.). 3-Isobutyl-1-methyl-xanthine (IBMX) stimulated a negative ISC and enhanced apical secretory K+ flux. Basolateral application of NPPB inhibited JRbB-->A fluxes, suggesting the interaction of K+ channels with NPPB-sensitive Cl- channels. The results are summarized in a transport model, suggesting apical Na+/K+/2Cl- co-transport, a dominant apical K+-secreting channel and basolaterally located Cl- and K+ channels. This study represents the first comprehensive characterization of ion transport processes across the lobster epipodite epithelium and indeed in any tissue within the branchial cavity of the American lobster.
Lucu
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Mount Desert Island Biological Laboratory, Salisbury Cove, ME 04672, USA. cedomil.lucu@unidu.hr
Towle
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D000825:Animal Structures / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D002712:Chlorides / Q000378:metabolism; D004573:Electrolytes / Q000378:metabolism; D015640:Ion Channel Gating / Q000502:physiology; D017136:Ion Transport; D008954:Models, Biological; D008121:Nephropidae / Q000033:anatomy & histology* / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D013997:Time Factors
D002712:Chlorides; D004573:Electrolytes; D012964:Sodium; D011188:Potassium