Pharmacological properties of excitation-contraction mechanisms in isolated mouse left atria

Effects of 4-aminopyridine (4-AP), nicardipine and ryanodine on the action potential and contractile force were examined in isolated mouse left atria. The mouse left atria had an action potential with an extremely short durat ion and two phases of repolarization; action potential duration at 50% repo larization was 6.7 +/- 0.4 ms (n = 15). The action potential duration, as w ell as contractile force, was increased by 4-AP (at 100 mu mol/l and 1 mmol /l). Nicardipine (3 mu mol/l), which is known to greatly reduce the contrac tile force in atria of most other experimental animal species, had no signi ficant effect on the action potential and decreased contractile force by on ly 40% in mouse atria. Ryanodine (10 nmol/l) decreased the contractile forc e by 90% of basal value. At 100 nmol/l, ryanodine slightly affected the act ion potential configuration, which could be explained by indirect effects t hrough inhibition of Ca2+ release from the sarcoplasmic reticulum. The extr emely short action potential duration and the highly sarcoplasmic reticulum -dependent contraction of the mouse atria appear to underlie its unique res ponse to agonists. Copyright (C) 2001 S. Karger AG. Basel.