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First published online April 23, 2004
Journal of Experimental Biology 207, 1779-1787 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00964

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The transepithelial voltage of the isolated anterior stomach of mosquito larvae (Aedes aegypti): pharmacological characterization of the serotonin-stimulated cells

H. Onken^*, S. B. Moffett and D. F. Moffett

School of Biological Sciences, Washington State University, Pullman, WA 99164-4236, USA

View larger version (14K): [in a new window]   Fig. 2. Time course of the transepithelial voltage of the anterior stomach of a fourth-instar mosquito larva (Aedes aegypti) normalized to the percentage of the control value (–20 mV). During the time period indicated by the horizontal boxes (1), dinitrophenol (2.5 mmol l-1) was present in the bath perfusate. Infusion mode was used throughout the experiment shown. At the arrow, the preparation was withdrawn from the perfusion pipette.

View larger version (15K): [in a new window]   Fig. 3. Time courses of the transepithelial voltage normalized to the percentage of the control value (–38 mV and –19 mV, respectively), showing the effects of substitution of Na+ (time period 1, N-methylglucamine) and Cl- (time period 2, gluconate). During the time periods indicated by w, perfusion of the anterior stomach preparation was changed to withdrawal mode, establishing the bathing solution also on the luminal side of the epithelium. Infusion mode was used during the rest of the time. At the arrow, the preparation was withdrawn from the perfusion pipette.

View larger version (9K): [in a new window]   Fig. 4. Time course of the transepithelial voltage normalized to the percentage of the control value (–19 mV), showing the effects of ouabain and concanamycin A. During the time period 1, ouabain (2.5 mmol l-1) was present in the bath perfusate. During the time period 1+2, ouabain (2.5 mmol l-1) and concanamycin A (10 µmol l-1) were present in the bath perfusate. Infusion mode was used throughout the experiments shown. At the arrow, the preparation was withdrawn from the perfusion pipette.

View larger version (13K): [in a new window]   Fig. 5. Time courses of the transepithelial voltage normalized to the percentage of the control value (–46 mV and –22 mV, respectively), showing the effects of ouabain (2.5 mmol l-1) during time period 1, of BaCl2 (5 mmol l-1) during time period 2 and of amiloride (0.2 mmol l-1) during time period 3. During the time period denoted w, perfusion of the preparation was changed to withdrawal mode, establishing the bathing solution also on the luminal side of the epithelium. Infusion mode was used during the rest of the time.

View larger version (16K): [in a new window]   Fig. 6. Time courses of the transepithelial voltage normalized to the percentage of the control value (–29 mV and –58 mV, respectively), showing the effects of DPC (0.5 mmol l-1) during time period 1 and of DIDS (0.1 mmol l-1) during time period 2. During the time periods denoted w, perfusion of the preparation was changed to withdrawal mode, establishing the bathing solution also on the luminal side of the epithelium. Infusion mode was used during the rest of the time.

View larger version (15K): [in a new window]   Fig. 1. Time courses of the transepithelial voltage (Vte) of the anterior stomach of a fourth-instar mosquito larva (Aedes aegypti). At arrow 1, the perfusion pipette was inserted into the anterior end of the anterior midgut. At arrow 2, the preparation was fixed on the pipette with a fine hair. At arrows 3–7, small slices (each approximately 10% of the initial length of the preparation) were cut off the open, posterior end of the preparation. At arrow 8, the remnant of the preparation was withdrawn from the pipette. During the time period indicated by the horizontal box, 0.2 µmol l-1 serotonin was present in the bathing medium. Infusion mode was used throughout the experiments shown.

View larger version (22K): [in a new window]   Fig. 7. Hypothetical transport model of NaHCO3 secretion and HCl absorption across the serotonin-stimulated cell population in the isolated and perfused anterior stomach of mosquito larvae (Aedes aegypti) proposed to be reflected in the outside negative transepithelial voltage (Vte). (A) Na+-independent part. Metabolic CO2 is hydrated and dissociates, accelerated by carbonic anhydrase (CA), into H+ and HCO3-. H+ are pumped by V-ATPases across the basolateral membrane to the hemolymph, resulting in hyperpolarization of the cellular electrical potential and in high cellular HCO3-. Cl-/HCO3- exchange across the luminal membrane is driven by the high cellular HCO3-. To explain the electrogenic nature of the overall process, anion channels are proposed to be present in the apical membrane, allowing Cl- recycling and/or electrogenic secretion of HCO3- driven by the cellular negativity. Cl- channels in the basolateral membrane allow transcellular absorption of Cl- ions (cf. Boudko et al., 2001a). (B) Na+-dependent part. In addition to energization of HCO3- secretion via apical anion exchange/channels (see A), the V-ATPase is proposed to energize transapical NaHCO3 secretion via electrogenic Na+/2–3HCO3- symporters. Na+/H+ exchangers in the basolateral membrane are considered to supply the cells with Na+ and to support the V-ATPases to drive H+ across the basolateral membrane. Paracellular secretion of Na+/absorption of Cl- driven by Vte is proposed to guarantee mass transport. See Discussion for further details.