AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 5 1190-R1198, Copyright © 1989 by American Physiological Society
Electrophysiological and cable parameters of perfused beetle malpighian tubules
L. C. Isaacson, S. W. Nicolson and D. W. Fisher
Department of Physiology, University of Cape Town Medical School, Observatory, South Africa.
Isolated perfused Malpighian tubules of the desert beetle Onymacris plana
(Coleoptera: Tenebrionidae) have been subjected to cable analysis under the
following conditions: control, adenosine 3',5'-cyclic monophosphate (cAMP),
corpora cardiaca homogenate (CCH), and high ambient K (130 mM). In
addition, we investigated possible effects of perfusate composition on
proximal transtubular potential (Vo) by reducing K, Na, or Cl or by adding
ouabain, furosemide, or dinitrophenol. The effects of cAMP, CCH, and high K
on Vo and cable parameters were consistent with increased fluid secretion,
i.e., diminished input and core resistances and increased virtual
short-circuit current, length constant, and luminal diameter. They differed
in that CCH had variable effects on Vo and high K did not reduce
transepithelial resistance. In terms of their effects on the parameters of
a simple equivalent electrical circuit, the responses to cAMP, CCH, and a
high ambient K concentration appear to be mediated by different mechanisms.
Alterations in perfusate composition were almost without effect.
