Physiologic Implications of the Hormonal Control of Ion Transport in Plants

The terrestrial robber crab Birgus latro L. regulates the composition of its final excretory product (termed P) depending on the availability of dietary salt by reabsorbing ions from urine passed over the gills. Laboratory and field-based studies investigated the nature of the mechanisms of control of this branchial ion uptake. B. latro were prepared such that their branchial chambers could be perfused with artificial urine, and the rate of ion transport from the artificial urine was determined. For B. latro acclimated to drinking fresh water, the rates of Na(+) and Cl(−) uptake were more than four times those of crabs drinking 70 % sea water. Crabs were injected with either saline carrier or the same solution containing either dopamine or dibutyryl cyclic AMP (db-cAMP) (final concentration 8.7×10(−)(7)mol l(−)(1)haemolymph). Dopamine and db-cAMP inhibited Na(+) and Cl(−) uptake in animals acclimated to fresh water and markedly reduced their gill Na(+)/K(+)-ATPase activity. Dopamine stimulated the production of cyclic AMP within the branchial epithelial cells. Dopamine, released from the pericardial organs, acts as a primary messenger, and cyclic AMP acts as a second messenger most likely promoting phosphorylation of membrane proteins. In contrast to aquatic brachyuran crabs, ion transport in B. latro, an anomuran, is controlled via an inhibitory effect. Terrestrial crabs normally have access to fresh water and must salvage salt from their urine, and a mechanism to down-regulate a normally active uptake system seems more appropriate to their ecology. Whether the control is stimulatory or inhibitory in the various air-breathing crabs may depend on the osmoregulatory abilities of their aquatic ancestors, but in either case has significant implications for the evolution of crustaceans to life on land. Further work must establish whether terrestrial brachyuran crabs are similar to B. latro and whether this crab is unique amongst the anomuran crabs.

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Ion Transport and Water Movement

Journal of Dental Research ◽

10.1177/00220345870660s106 ◽

1987 ◽

Vol 66 (1_suppl) ◽

pp. 638-647 ◽

Cited By ~ 17

Author(s):

J. R. Martinez

Keyword(s):

Cell Membrane ◽

Ion Transport ◽

Water Movement ◽

Transport Processes ◽

Hormonal Control ◽

Dual Process ◽

Transport Systems ◽

Osmotic Gradient ◽

Basolateral Cell Membrane ◽

Ion Movements

Secretion of water and electrolytes in salivary glands occurs by a dual process involving the formation of a plasma-like, isotonic primary-secretion in salivary acini and its subsequent modification in salivary-ducts by the removal and addition of specific ions. The mechanisms underlying the formation of primary acinar secretion have been investigated with a number of experimental approaches such as electrophysiology, the measurement of ion transport in gland fragments and dispersed acinar cells, and the evaluation of the ionic requirements for secretion in isolated, perfused gland preparations. The accumulated evidence suggests that salivary secretion is formed by a complex interaction between passive and active ion movements across acinar cell membranes, resulting in the trans-acinar movement of CI and Na+ and, by the osmotic gradient which develops, of water. A major consequence of stimulation is the release of K + through Ca++ -and voltage-sensitive channels and its subsequent recycling back into the cells by ouabain- and furosemide-sensitive transport systems. This results in NaCl uptake across the basolateral cell membrane and the subsequent efflux of CI through luminal membrane channels, which also appear to be sensitive to cellular Ca + +. The rates of these various ion movements appear to be, therefore, closely linked and interdependent. Ductal modification of the primary secretion has been studied in microperfused duct preparations. The evidence likewise indicates that it involves interactions between complex conductance pathways in the luminal cell membrane and a Na, K pump present in the basolateral cell membrane and that it is under autonomic and hormonal control. Activation of ductal transport mechanisms results in NaCl reabsorption and KHCO3 secretion. Final saliva thus differs from primary secretion in electrolyte composition and, because water permeability is low in the duct epithelium, becomes hypotonic. Alterations in fluid and electrolyte secretion such as those observed in disease can result, therefore, from disturbances in one or more of these complex transport processes in acinar or duct cells.

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Primary culture of duck salt gland. II. Neurohormonal stimulation of active transport

AJP Cell Physiology ◽

10.1152/ajpcell.1985.249.1.c41 ◽

1985 ◽

Vol 249 (1) ◽

pp. C41-C47 ◽

Cited By ~ 11

Author(s):

R. J. Lowy ◽

D. C. Dawson ◽

S. A. Ernst

Keyword(s):

Ion Transport ◽

Short Circuit ◽

Primary Cultures ◽

Short Circuit Current ◽

Salt Gland ◽

Hormonal Control ◽

Regulatory Control ◽

Secretory Cells ◽

Active Ion Transport ◽

Secretory Transport

Primary cultures of structurally polarized sheets of avian salt gland secretory cells were mounted in Lucite chambers for transmural electrophysiological analysis. Transmural resistance values increased during the first 3 days of culture to 293 +/- 35 omega X cm2 and then decreased slowly thereafter. There was little short-circuit current (Isc) in the absence of secretagogues. Serosal addition of either carbachol or epinephrine resulted in a Isc consistent with positive charge flow from mucosa to serosa, thus demonstrating that these cell layers were capable of active ion transport in response to either cholinergic or adrenergic neurohormonal stimulation. Serosal ouabain or furosemide abolished the response to either agonist, while theophylline enhanced the response. Receptor specificity for the electrical responses was shown by selective inhibition of carbachol- and epinephrine-induced Isc by atropine and propranolol, respectively. The results demonstrate that these primary epithelial cell cultures are capable of active ion transport and are sensitive to known inhibitors of secretory transport, and suggest that intracellular coupling mechanisms for hormonal control are retained in culture. These cultures should be useful for studying mechanisms of ion secretory transport and their regulatory control.

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Ion Transport and Water Movement

Journal of Dental Research ◽

10.1177/00220345870660s206 ◽

1987 ◽

Vol 66 (2_suppl) ◽

pp. 638-647 ◽

Cited By ~ 58

Author(s):

J. R. Martinez

Keyword(s):

Cell Membrane ◽

Ion Transport ◽

Water Movement ◽

Transport Processes ◽

Hormonal Control ◽

Dual Process ◽

Transport Systems ◽

Osmotic Gradient ◽

Basolateral Cell Membrane ◽

Ion Movements

Secretion of water and electrolytes in salivary glands occurs by a dual process involving the formation of a plasma-like, isotonic primary-secretion in salivary acini and its subsequent modification in salivary-ducts by the removal and addition of specific ions. The mechanisms underlying the formation of primary acinar secretion have been investigated with a number of experimental approaches such as electrophysiology, the measurement of ion transport in gland fragments and dispersed acinar cells, and the evaluation of the ionic requirements for secretion in isolated, perfused gland preparations. The ac-cumulated evidence suggests that salivary secretion is formed by a complex interaction between passive and active ion movements across acinar cell membranes, resulting in the trans-acinar movement of Cl and Na* and, by the osmotic gradient which develops, of water. A major consequence of stimulation is the release of K+ through Ca++ -and voltage-sensitive channels and its subsequent recycling back into the cells by ouabain- and furosemide-sensitive transport systems. This results in NaCl uptake across the basolateral cell membrane and the subsequent efflux of Cl through luminal membrane channels, which also appear to be sensitive to cellular Ca++. The rates of these various ion movements appear to be, therefore, closely linked and interdependent. Ductal modification of the primary secretion has been studied in microperfused duct preparations. The evidence likewise indicates that it involves interactions between complex conductance pathways in the luminal cell membrane and a Na, K pump present in the basolateral cell membrane and that it is under autonomic and hormonal control. Activation of ductal transport mechanisms results in NaCl reabsorption and KHCO3 secretion. Final saliva thus differs from primary secretion in electrolyte composition and, because water permeability is low in the duct epithelium, becomes hypotonic. Alterations in fluid and electrolyte secretion such as those observed in disease can result, therefore, from disturbances in one or more of these complex transport processes in acinar or duct cells.

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