After effects of perfusion with glucose-insulin-potassium solution on the membrane current and tension components of frog atrial muscle.

As glucose-insulin-potassium solution (GIK) has been used as clinical cardioplegia during open heart surgery, we studied the fundamental effects of GIK on the electrical and mechanical activities of the bullfrog atrial muscle under voltage clamped and unclamped conditions by the double sucrose-gap method. GIK produced an immediate disappearance of the action potential and twitch tension with pronounced depolarization accompanied by transient contracture. Reperfusion with normal Ringer's solution after GIK perfusion (30-180 min) resulted in recovery of the action potential, with an initial lengthening followed by a sustained shortening in duration. Recovery of twitch tension was incomplete, and perfusion with GIK for a longer period caused stronger suppression. Voltage clamp studies revealed that after removal of GIK, the slow inward current (Is) and Is-dependent tension were markedly depressed, while the delayed outward current (Ix) was augmented. The fast inward current (INaf), background current (Ik1), and Is-independent tension gradually recovered to the control levels. Perfusion with low Ca Ringer's solution or verapamil Ringer's solution for 10 min at the initial reperfusion phase significantly improved the recovery of Is and the Is-dependent tension. These results indicate that the after-effects of GIK are mainly governed by Ca influx at the initial reperfusion phase. Therefore, a lowering of the Ca influx in this period is expected to produce a beneficial effect on cardiac function after GIK treatment.