title: Different modes of electrogenic Na+ absorption in the coprodeum of the chicken embryo: role of extracellular Ca2+.
abstract: Transepithelial electrogenic Na+ transport (INa) was investigated in the coprodeum of 20-days-old chicken embryos in Ussing chambers. Short circuit current (Isc) and transepithelial resistance (Rt) were 14.7 +/- 4.8 microA.cm-2 (n = 12) and 0.53 +/- 0.09 k omega.cm-2 (n = 12), respectively. INa was calculated from changes in Isc by substitution of mucosal Na+ by (N-methyl-D-glucamine) (NMDG). Isc inversed during Na+ removal, and INa was found to be 27.8 +/- 4.7 microA.cm-2 (n = 12). Amiloride (100 mumol.l-1) inhibited only about 60% of INa. Analysis of Isc fluctuations revealed a Lorentzian component in the power density spectrum with a corner frequency of about 57 Hz. This component was not correlated to INa, and its origin is still unclear. Removal of mucosal Ca2+ increased INa about 2.5-fold due to an increase of the amiloride-insensitive component of INa in additionally investigated adult tissues. The results clearly show that this is due to a non-selective cation channel with an "apparent" order of selectivity Cs+ greater than Na+ = K+ greater than Rb+ greater than Li+. The Ca2+ concentration required to block 50% of the Isc was about 18 mumol.l-1. The IscCa could also be suppressed by other divalent cations such as Mg2+ and Ba2+. Additionally, an INa-linked Lorentzian component occurred which dominated the control spectrum with a significantly higher corner frequency (about 88 Hz). The results indicate that Na+ absorption in the coprodeum of the chicken embryo is more complex than in adult hens.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Institut für Veterinärphysiologie, Freie Universität Berlin, Federal Republic of Germany.
authors.forename: M
authors.initials: M
authors.lastname: Heinz
authors.forename: R
authors.initials: R
authors.lastname: Krattenmacher
authors.forename: B
authors.initials: B
authors.lastname: Hoffmann
authors.forename: W
authors.initials: W
authors.lastname: Clauss
mesh_terms: D000042:Absorption; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002642:Chick Embryo; D002988:Cloaca / Q000378:metabolism*; D004563:Electrochemistry; D004848:Epithelium / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism
chemical_list: D015222:Sodium Channels; D000584:Amiloride; D012964:Sodium; D002118:Calcium