|
| |
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
Ion transport across posterior gills of hyperosmoregulating shore crabs (Carcinus maenas): amiloride blocks the cuticular Na+ conductance and induces current-noise
1 Departmento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Avenida Bandeirantes 3900, 14040-901 Ribeirão Preto, SP, Brasil and
2 Biologische Anstalt Helgoland, Zentrale Hamburg, Notkestrasse 31, 22607 Hamburg, Germany
*e-mail: onkenh{at}ffclrp.usp.br
Accepted 29 November 2001
Split gill lamellae and gill cuticles of shore crabs (Carcinus maenas) adapted to 10 
salinity were mounted in a modified Ussing-type chamber. With NaCl saline on both sides, split gill lamellae generated a short-circuit current (Isc) of –301±16 µA cm–2 at a conductance (Gte) of 40±2 mS cm–2. The net influxes of Na+ and Cl– were 8.3±2.6 and 18.2±2.7 µmol cm–2 h–1, respectively. External amiloride (100 µmol l–1) reduced Gte to approximately 50 % of the original value at unchanged Isc; Cl– fluxes remained unaffected, whereas Na+ fluxes were markedly reduced by 70–80 %. The Isc in the presence of external amiloride was almost completely inhibited by internal ouabain. At a clamp voltage of 50 mV (outside-positive), a positive current was measured at unchanged Gte. Under these conditions, amiloride reduced the current and conductance at half-maximal concentrations of 3.6 and 2.0 µmol l–1, respectively. At outside-positive voltages, but not under short-circuit conditions, external amiloride induced Lorentzian components in the power density spectra. The amiloride-dependent changes in the corner frequency (linear) and of the low-frequency plateau (‘bell-shaped’) were as expected for channel blockade by amiloride with pseudo-first-order kinetics. With an outside-positive clamp voltage of 50 mV across isolated cuticles, a positive cuticular current (Icut) of 25 188±3791 µA cm–2 and a cuticular conductance (Gcut) of 547±76 mS cm–2 were measured. External amiloride reduced Icut and Gcut at half-maximal concentrations of 0.7 and 0.6 µmol l–1, respectively. Amiloride-induced current-noise analysis gave similar results to those observed with split gill lamellae. Ion-substitution experiments with isolated cuticles further support inhibition by external amiloride of the cuticular Na+ conductance of shore crab gills and not amiloride-sensitive transporters (Na+ channels or Na+/H+ antiports) in the apical membrane.
Key words: amiloride, shore crab, Carcinus maenas, conductance, gills, cuticle, ion flux, NaCl absorption, short-circuit current, current-noise analysis, Ussing chamber.
This article has been cited by other articles:
|
|
 |
|
  M. Tresguerres, S. K. Parks, S. E. Sabatini, G. G. Goss, and C. M. Luquet Regulation of ion transport by pH and [HCO3-] in isolated gills of the crab Neohelice (Chasmagnathus) granulata Am J Physiol Regulatory Integrative Comp Physiol, March 1, 2008; 294(3): R1033 - R1043. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. Weihrauch, S. Morris, and D. W. Towle Ammonia excretion in aquatic and terrestrial crabs J. Exp. Biol., December 15, 2004; 207(26): 4491 - 4504. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Morris and M. D. Ahern Regulation of urine reprocessing in the maintenance of sodium and water balance in the terrestrial Christmas Island red crab Gecarcoidea natalis investigated under field conditions J. Exp. Biol., August 15, 2003; 206(16): 2869 - 2881. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. Onken, M. Tresguerres, and C. M. Luquet Active NaCl absorption across posterior gills of hyperosmoregulating Chasmagnathus granulatus J. Exp. Biol., March 15, 2003; 206(6): 1017 - 1023. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. Weihrauch, A. Ziegler, D. Siebers, and D. W. Towle Active ammonia excretion across the gills of the green shore crab Carcinus maenas: participation of Na+/K+-ATPase, V-type H+-ATPase and functional microtubules J. Exp. Biol., September 15, 2002; 205(18): 2765 - 2775. [Abstract] [Full Text] [PDF]
|
|
