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First published online October 7, 2004
Journal of Experimental Biology 207, 3935-3944 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01221

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Characterization of the voltage-activated currents in cultured atrial myocytes isolated from the heart of the common oyster Crassostrea gigas

Jean-Pierre Pennec^*, Hélène Talarmin, Mikaël Droguet, Marie-Agnès Giroux-Metgès, Maxime Gioux and Germaine Dorange

EA 3879, Unité de Physiologie Comparée et Intégrative, Institut de Synergie des Sciences et de la Santé, 22 avenue Camille Desmoulins, CS93837, 29238, Brest-cedex 3, France

View larger version (34K): [in a new window]   Fig. 1. (A) Upper trace: sum of the currents recorded in cultured atrial cells from oyster. Inward current, mainly the fast sodium current, is classically represented downwards, and outward currents, mainly the potassium currents, upwards. Lower trace: voltage steps imposed to the membrane. Depolarizing steps are upwards. Horizontal bar, 1 ms; vertical bars, 0.1 nA (top) and 40 mV (bottom). (B) Upper trace: sum of the fast inactivating and of the delayed potassium current. Lower trace: voltage steps applied to the membrane. Horizontal bar, 10 ms; vertical bars, 0.1 nA (top) and 60 mV (bottom). (C) Upper trace: delayed potassium current recorded after inhibition of the fast inactivating potassium current by 4-aminopyridine. Lower trace: voltage steps applied to the membrane. Horizontal bar, 10 ms; vertical bars, 0.1 nA (top) and 60 mV (bottom). (D) Current–voltage relationship of the delayed potassium current. The maximum conductance is calculated from the slope of the linear part.

View larger version (33K): [in a new window]   Fig. 2. (A) Upper trace: fast inactivating potassium current recorded after inhibition of the delayed potassium current by tetraethyl ammonium. Lower trace: voltage steps applied to the membrane. Horizontal bar, 1 ms; vertical bars, 0.1 nA (top) and 40 mV (bottom). (B) Upper trace: fast inactivating potassium current recorded after inhibition of the delayed potassium current by tetraethyl ammonium. Lower trace: inhibition of the fast inactivating potassium current by 4-amino pyridine. Horizontal bar, 1 ms, vertical bar, 0.1 nA. (C) Inhibition of the fast inactivating potassium current by depolarizing pulses applied to the membrane before the test pulse. Horizontal bar, 1 ms, vertical bar, 0.1 nA. (D) Inhibition curve of the IK fast current by depolarizing pulses. Experimental points are fitted onto a Boltzman-type equation. Vertical: normalized current expressed as measured current/maximum measured current. Horizontal: depolarizing pulse expressed as minus the pipette voltage Vpip.

View larger version (16K): [in a new window]   Fig. 3. Current–voltage relationship of the fast inactivating potassium current. The maximum conductance is calculated from the slope of the linear part (see text).

View larger version (21K): [in a new window]   Fig. 4. (A) Upper trace: maxi potassium current recorded after inhibition of the fast inactivating potassium current by 4-aminopyridine. Lower trace: voltage steps applied to the membrane. Horizontal bar, 10 ms; vertical bars, 0.2 nA (top) and 60 mV (bottom). (B) Effect of charybdotoxin (CHTX) on the spontaneous beating rate of atrial cultured cells from oyster. Vertical: beating frequency. Horizontal: CHTX addition in Petri dishes corresponding to a final concentration of: 5x10–6, 10–5, 1.5x10–6 mol l–1. All the CHTX values are significantly different from the control.

View larger version (16K): [in a new window]   Fig. 5. Example of a recording of the fast sodium current after tetraethyl ammonium and 4-aminopyridine treatment. Horizontal bar, 1 ms; vertical bars, 0.1 nA (top) and 40 mV (bottom).

View larger version (53K): [in a new window]   Fig. 6. (A) Example of a recording of the calcium inward current after treatment with 40 mmol l–1 tetraethyl ammonium chloride, 10–6 mol l–1 TTX and 40 mmol l–1 4-aminopyridine treatment. (B) Effect of the addition of 10–5 mol l–1 of serotonin (5HT) on the calcium current. (C) Blockade of the calcium current after addition of cobalt ions in the medium bathing the cells and in the pipette. (D) Imposed voltages. Vertical bars, 0.1 nA (A–C) and 60 mV (D); horizontal bar, 10 ms.

View larger version (14K): [in a new window]   Fig. 7. Effect of serotonin (5HT) on the spontaneous beating rate of in vitro atrial cultured cells. Vertical: percent of the maximum effect. Horizontal: serotonin corresponding to a final concentration ranging from of 10–11 to 10–7 mol l–1. A significant increase (P<0.05) was observed at concentrations of 5HT equal or higher than 10–9 mol l–1. Values obtained with concentrations equal or higher than 10–6 mol l–1 are not plotted because the beatings became erratic, and the cells were detaching themselves from the plastic bottom of the Petri dishes, showing a toxic effect at such concentrations.

View larger version (7K): [in a new window]   Fig. 8. Example of a transient inward calcium current following a fast outward potassium current. The cell was treated with tetraethyl ammonium chloride. Vertical bars, 0.1 nA (top) and 40 mV (bottom); horizontal bar, 10 ms.