scholarly journals Paracellular and transcellular routes for water and solute movements across insect epithelia

1983 ◽  
Vol 106 (1) ◽  
pp. 231-253 ◽  
Author(s):  
M. J. O'Donnell ◽  
S. H. Maddrell
Keyword(s):  
Ion Transport ◽  
Organic Molecules ◽  
Water Movement ◽  
Fluid Secretion ◽  
Malpighian Tubules ◽  
Transport Mechanisms ◽  
Osmotic Permeability ◽  
Passive Response ◽  
Active Ion Transport ◽  
Intercellular Clefts

Because the frontal area of the intercellular clefts in Malpighian tubules is small, and the osmotic permeability of the cell membranes is large, the route for transepithelial water movement during fluid secretion is transcellular. Water movements appear to be a passive response to osmotic gradients of a few mosmol 1(−1) produced in the cells and in he lumen by active ion transport. The excretory functions of Malpighian tubules are discussed in relation to recent analyses of the routes of passive permeation for non-electrolytes. Uncharged molecules smaller than a disaccharide appear to move at significant rates through the cells whereas molecules as large as inulin traverse the epithelium by a paracellular path. In addition there are specific active transport mechanisms for a variety of organic molecules. The routes and mechanisms proposed for water and solute movements are discussed in relation to comparable studies in other epithelia.

Membrane dynamics in insect malpighian tubules

1989 ◽  
Vol 257 (5) ◽  
pp. R967-R972
Author(s):  
T. J. Bradley
Keyword(s):  
Ion Transport ◽  
Driving Force ◽  
Fluid Secretion ◽  
Membrane Dynamics ◽  
Malpighian Tubules ◽  
Membrane Insertion ◽  
Cation Pump ◽  
Active Ion Transport ◽  
Urine Formation ◽  
Apical Membranes

Urine formation in insects occurs in the Malpighian tubules by means of active ion transport and osmotically coupled water flow. The rates of urine formation can vary with time and can be modulated by diuretic hormones, developmental events, and intracellular parasitism. This paper reviews a number of recent studies in which it has been demonstrated that variations in transport rate are associated with substantial changes in tubule ultrastructure in the form of membrane insertion into and deletion from the apical microvilli. The principal driving force for fluid movement in Malpighian tubules is thought to be a common cation pump located in the apical membranes. It is proposed that modulation of the apical microvillar membrane may reflect regulation by the cells of the number of common cation pump units involved in fluid secretion.

The anterior and posterior ‘stomach’ regions of larval Aedes aegypti midgut: regional specialization of ion transport and stimulation by 5-hydroxytryptamine

1999 ◽  
Vol 202 (3) ◽  
pp. 247-252 ◽  
Author(s):  
T.M. Clark ◽  
A. Koch ◽  
D.F. Moffett
Keyword(s):  
Steady State ◽  
Aedes Aegypti ◽  
Ion Transport ◽  
Malpighian Tubules ◽  
Transport Mechanisms ◽  
Regional Specialization ◽  
Negative Deflection ◽  
Electrical Polarity

The ‘stomach’ region of the larval mosquito midgut is divided into histologically distinct anterior and posterior regions. Anterior stomach perfused symmetrically with saline in vitro had an initial transepithelial potential (TEP) of −66 mV (lumen negative) that decayed within 10–15 min to a steady-state TEP near −10 mV that was maintained for at least 1 h. Lumen-positive TEPs were never observed in the anterior stomach. The initial TEP of the perfused posterior stomach was opposite in polarity, but similar in magnitude, to that of the anterior stomach, measuring +75 mV (lumen positive). This initial TEP of the posterior stomach decayed rapidly at first, then more slowly, eventually reversing the electrical polarity of the epithelium as lumen-negative TEPs were recorded in all preparations within 70 min. Nanomolar concentrations of the biogenic amine 5-hydroxytryptamine (5-HT, serotonin) stimulated both regions, causing a negative deflection of the TEP of the anterior stomach and a positive deflection of the TEP of the posterior stomach. Phorbol 12,13-diacetate also caused a negative deflection of the TEP of the anterior stomach, but had no effect on the TEP of the posterior stomach. These data demonstrate that 5-HT stimulates region-specific ion-transport mechanisms in the stomach of Aedes aegypti and suggest that 5-HT coordinates the actions of the Malpighian tubules and midgut in the maintenance of an appropriate hemolymph composition in vivo.

Measurements of osmotic permeability in the Malpighian tubules of an insect, Rhodnius prolixus Stål

1982 ◽  
Vol 216 (1204) ◽  
pp. 267-277 ◽  
Keyword(s):  
Ion Transport ◽  
Experimental Method ◽  
Malpighian Tubule ◽  
Rhodnius Prolixus ◽  
Malpighian Tubules ◽  
Unstirred Layer ◽  
Osmotic Permeability

(i) With use of a novel experimental method, an improved estimate has been obtained for the value of the osmotic permeability ( P os ) of Rhodnius Malpighian tubules, 4.3 x 10 -3 cm s -1 osmol -1 l. Corrections for unstirred layer effects permit a further 35% increase in the value of P os , to 5.8 x 10 -3 cm s -1 osmol -1 l. (ii) In the lower Malpighian tubule, P os decreases from 3.4 x 10 -3 cm s -1 osmol -1 l at the junction with the upper Malpighian tubule to 0.4 x 10 -3 cm s -1 osmol -1 l at the junction with the gut. In lower tubules stimulated with 5-HT, P os is reduced over most of their length by about 50% . It is suggested that reduced values of P os in the lower portions of the lower tubule prevent water movements accompanying 5-HT-stimulated KCl resorption over the same area of the tubule. (iii) Values of P os in the upper segment of the upper tubule are discussedin relation to proposed mechanisms for coupling water movements to ion transport during isosmotic secretion by the tubule.

Dibutyryl cAMP activates bumetanide-sensitive electrolyte transport in Malpighian tubules

1991 ◽  
Vol 261 (3) ◽  
pp. C521-C529 ◽  
Author(s):  
J. L. Hegarty ◽  
B. Zhang ◽  
T. L. Pannabecker ◽  
D. H. Petzel ◽  
M. D. Baustian ◽  
...  
Keyword(s):  
Yellow Fever ◽  
Apical Membrane ◽  
Basolateral Membrane ◽  
Fluid Secretion ◽  
Ringer Solution ◽  
Malpighian Tubules ◽  
Membrane Voltage ◽  
Dibutyryl Camp ◽  
K Secretion ◽  
Transepithelial Voltage

The effects of dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP) and bumetanide (both 10(-4) M) on transepithelial Na+, K+, Cl-, and fluid secretion and on tubule electrophysiology were studied in isolated Malpighian tubules of the yellow fever mosquito Aedes aegypti. Peritubular DBcAMP significantly increased Na+, Cl-, and fluid secretion but decreased K+ secretion. In DBcAMP-stimulated tubules, bumetanide caused Na+, Cl-, and fluid secretion to return to pre-cAMP control rates and K+ secretion to decrease further. Peritubular bumetanide significantly increased Na+ secretion and decreased K+ secretion so that Cl- and fluid secretion did not change. In bumetanide-treated tubules, the secretagogue effects of DBcAMP are blocked. In isolated Malpighian tubules perfused with symmetrical Ringer solution, DBcAMP significantly hyperpolarized the transepithelial voltage (VT) and depolarized the basolateral membrane voltage (Vbl) with no effect on apical membrane voltage (Va). Total transepithelial resistance (RT) and the fractional resistance of the basolateral membrane (fRbl) significantly decreased. Bumetanide also hyperpolarized VT and depolarized Vbl, however without significantly affecting RT and fRbl. Together these results suggest that, in addition to stimulating electroconductive transport, DBcAMP also activates a nonconductive bumetanide-sensitive transport system in Aedes Malpighian tubules.

A cellular pathway for Cl− during fluid secretion in ant Malpighian tubules: Evidence from ion-sensitive microelectrode studies?

1995 ◽  
Vol 41 (8) ◽  
pp. 695-703 ◽  
Author(s):  
S. Dijkstra ◽  
A. Leyssens ◽  
E. Van Kerkhove ◽  
W. Zeiske ◽  
P. Steels
Keyword(s):  
Fluid Secretion ◽  
Malpighian Tubules ◽  
Cellular Pathway
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