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Electrophysiology of posterior, NaCl-absorbing gills of Chasmagnathus granulatus: rapid responses to osmotic variations

M. Tresguerres^1,*, H. Onken², A. F. Pérez¹ and C. M. Luquet¹

¹ Dept Biodiversity and Experimental Biology, F.C.E.N. University of Buenos Aires, Pab. II, Ciudad Universitaria, C1428EHA Buenos Aires, Argentina
² Dept Biological Sciences, F.F.C.L.R.P. University of Sao Paulo, Brazil

View larger version (8K): [in a new window]   Fig. 1. Effects of reduced ion concentrations [(A) chloride, (B) sodium] and reduced osmolarity on the transepithelial potential difference (Vte) across isolated posterior gills of Chasmagnathus granulatus acclimated to 2 salinity. Mean + S.E.M. of eight values are given in each column. Asterisks indicate statistical differences (P<0.05). Isosmotic: 517.5 mmol l-1 Cl- and 470.5 mmol l-1 Na+ (1045 mosmol l-1). Hyposmotic: 344.4 mmol l-1 Cl- and 314.5 mmol l-1 Na+ (698.6 mosmol l-1). Clred: chloride concentration of Hyposmotic saline, but osmolarity of Isosmotic saline. Nared: sodium concentration of Hyposmotic saline, but osmolarity of Isosmotic saline.

View larger version (13K): [in a new window]   Fig. 2. Representative time-course of the transepithelial potential difference (Vte) across an isolated perfused posterior gill during a typical osmolarity change experiment. The arrows indicate application of the different treatments. Isosmotic: 1045 mosmol l-1; Hyposmotic: 698.6 mosmol l-1; Hyposucrose1: Hyposmotic saline plus 60 mmol l-1 sucrose (758.6 mosmol l-1); Isosucrose: Hyposmotic saline plus 345.4 mmol l-1 sucrose (same osmolarity as Isosmotic saline).

View larger version (7K): [in a new window]   Fig. 3. Effect of osmotic manipulations on the hemolymph side of isolated posterior gills on the transepithelial potential difference (Vte). (A) Response of Vte to gradually reduced osmolarities. The data are given as percentages (± S.E.M.) of the Vte increase with Hyposmotic saline (100% response). N=20. (B) Response of Vte to ion concentration change at constant or reduced osmolarity. Mean ± S.E.M. of five values are given in each column. Asterisk indicates statistical difference (P<0.05). Isosmotic: 1045 mosmol l-1; Hyposmotic: 698.6 mosmol l-1; Isosucrose: Hyposmotic saline plus 345.4 mmol l-1 sucrose (same osmolarity as Isosmotic saline).

View larger version (11K): [in a new window]   Fig. 4. Time-course of the short-circuit current (Isc) across a split gill lamellae of a posterior gill (representative of three trials). The arrows indicate application of the different treatments. Isosmotic: 1045 mosmol l-1; Hyposmotic: 698.6 mosmol l-1; Isosucrose: Hyposmotic saline plus 345.4 mmol l-1 sucrose (same osmolarity as Isosmotic saline).

View larger version (13K): [in a new window]   Fig. 5. Specific activity of the Na+/K+-ATPase in homogenates obtained from gills perfused with isosmotic (Isosucrose) or with Hyposmotic saline. Isosucrose: 1045 mosmol l-1; Hyposmotic: 698.6 mosmol l-1. Mean ± S.E.M. of five values are given in each column. Asterisk indicates statistical difference (P<0.05).

View larger version (11K): [in a new window]   Fig. 6. Time-course of the transepithelial potential difference (Vte) across an isolated perfused posterior gill (representative of five trials). (A) Theophylline sustains the elevated Vte caused by forskolin. (B) Theophylline partially sustains the elevated Vte caused by Hyposmotic saline. Arrows indicate application of the different treatments. Iso + Theo: Isosmotic saline plus theophylline (2.5 mmol l-1); Iso + Forsk: Isosmotic saline plus forskolin (0.01 mmol l-1); Hypo + Theo: Hyposmotic saline plus theophylline (2.5 mmol l-1).

View larger version (8K): [in a new window]   Fig. 7. Effects of the interaction between osmotic variations and theophylline on the transepithelial potential difference (Vte) in isolated posterior gills. Mean ± S.E.M. of five values are given in each column. The different letters indicate statistical differences among treatments (P<0.05). Iso + Theo: Isosmotic saline plus theophylline (2.5 mmoll-1). Hypo + Theo: Hyposmotic saline plus theophylline (2.5 mmoll-1). Iso + Theo II: after perfusing with Hyposmotic saline plus theophylline.

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