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Journal of Experimental Biology 123,71-92 (1986)
Published by Company of Biologists 1986

Transcellular and Paracellular Flow of Water During Secretion in the Upper Segment of the Malpighian Tubule of Rhodnius Prolixus: Solvent Drag of Molecules of Graded Size

GUILLERMO WHITTEMBURY 1, ANGELA C. BIONDI 2, AZAEL PAZ-ALIAGA 3, HENRY LINARES 1, VALENTÍN PARTHE 1, and NANCY LINARES 1

1 Centro de Biofísica y Bioquímica, Instituto Venezolano de Investigaciones Científicas, IVIC, Caracas, Venezuela
2 Centro de Biofísica y Bioquímica, Instituto Venezolano de Investigaciones Científicas, IVIC, Caracas, Venezuela; Instituto de Química-Física, Facultad de Bioquímica, Química y Farmacia, Universidad Tucumáin, San Miguel de Tucumán, Argentina
3 Centro de Biofísica y Bioquímica, Instituto Venezolano de Investigaciones Científicas, IVIC, Caracas, Venezuela; Departamento de Fisiología, Universidad de San Agustín de Arequipa, Arequipa, Perú

The following molecules graded in size were added to the fluid bathing the blind end of the upper segment of the Malpighian tubules of Rhodnius: urea (U), erythritol (E), mannitol (M), L-glucose (G), sucrose (S), polyethyleneglycol 800 (PEG), raffinose (R), inulin (I) and dextran 15000–18000 (D). U, E, M and G distribute themselves within the cell and the extracellular space, while S, PEG, R, I and D are exclusively extracellular. In addition, the net secretory flow (Jnm8) of these probes was studied as a function of the net secretory volume flow (Jv). Jn8, is made up of a diffusive component (Jd8), mainly due to unstirred layer effects, and of a convective component (Jc8), due to the drag (entrainment) of the probes by the water flow. The relative contribution of Jd8 and of Jc8 for each probe was studied as a function of Jv. It was found that Jc8 >> Jd8 for U, E, M, G, S and PEG. Therefore these probes are dragged by water. On the other hand Jd8 = Jn8 for R, I and D, which are not entrained. It is concluded that water flows via extracellular pathways since S and PEG, which are true extracellular probes, are entrained by solvent. In addition to extracellular pathways, it is suggested that the transcellular structures described by Wessing (1965) and Bergeron et al. (1985) could also be the sites of solute-solvent coupling

Key words: paracellular flow, Malpighian tubules, secretion, epithelia

Submitted on January 3, 1986






© The Company of Biologists Ltd 1986