ANIMALS AND METHODS
In order to elucidate whether the defibrillating properties of tedisamil can also be related to enhancement of intercellular synchronization, the present study was designed to examine the effect of tedisamil on intercellular coupling in a ventricular strip of guinea pig heart.
Ten male guinea pigs, weighing 300 to 400 g, were sacrificed by stunning followed by carotid exsanguination. The hearts were quickly isolated. A muscle strip (4×4 mm) was cut from the right ventricular free muscle and superfused in a tissue bath with normal Tyrode’s solution bubbled with 95% oxygen and 5% carbon dioxide at 37°C. After superfusion for 20 mins, the solution was switched to one of the following test solutions: hypoxic Tyrode’s solution (without bubbling of oxygen); oxygenated high Ca2+ (6 mM) solution; hypoxic solution containing 0.1 |JM tedisamil; oxygenated high Ca2+ solution containing 0.1 to 0.5 |JM tedisamil.
After 20 mins of superfusion with either normal oxygenated Tyrode’s solution or each of the test solutions, 5% Lucifer yellow CH dye (Sigma-Aldrich, Tokyo, Japan) was injected into a cell (three to five in each) to visualize intercellular coupling. Injection was by applying negative current (-10 nA) pulses (1 s duration at 0.5 Hz) for 3 to 5 mins through a glass microelectropipette (tip resistance of 100 to 140 mQ). Wholemount preparations were investigated under a fluorescent microscope immediately after dye injection, and the spread of the dye to neighbouring cells was photographed.
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