Chronic Administration of Amiodarone Does Not Affect Na⁺/Ca²⁺ Exchange Current in Guinea Pig Cardiac Ventricular Myocytes

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We investigated chronic effects of amiodarone on Na⁺/Ca²⁺ exchange current (I_NCX) and on the level of Na⁺/Ca²⁺ exchanger (NCX1) mRNA in guinea pig ventricular myocytes using the whole-cell clamp technique and RT-PCR analysis, respectively. Guinea pigs were intraperitoneally injected with 80 mg/kg per day of amiodarone or the vehicle (saline) for 1 or 4 weeks. Single ventricular cells were isolated from the hearts of both groups of animals. Action potential duration at 90% repolarization level was prolonged to 143% and 165% of the control values by treatment with amiodarone for 1 and 4 weeks, respectively. I_NCX density and the level of NCX1 mRNA were not significantly changed by chronic treatment with amiodarone. The level of thyroid hormone (T₄) within the blood was not changed by the treatments. These results suggest that chronic treatment with amiodarone does not affect the Na⁺/Ca²⁺ exchanger, with respect to the level of its mRNA and current density in guinea pig ventricular myocytes.