The effect of glycine, structurally the most simple amino acid was investigated on the electrophysiological characteristics of the isolated superfused atrial muscle and sinus node cells of the rabbit heart. Superfusion of the sinus node cell with glycine solution (3, 5 and 8 mM) produced concentration-dependent increments of OS (overshoot potential) and MDP (maximum diastolic potential). Generally action potential amplitude increased as a result of greater increment of OS than that of MDP. The changes in action potential of the sinus node cell peaked in 7 ~ 10 minutes after onset of superfusioin. On the contrary to the response to intravenously administered glycine, the rate of spontaneous firing of sinus node cell was invariably increased following superfusion with glycine. Action potential duration manifested as APD60 (time to 60% repolarization) was significantly shortened by glycine. And the electrophysiological effects of glycine on the atrial muscle cell were similar to that on the sinus node cells. The results of present study suggest that glycine can exert direct effects on the atrial muscle and sinus node cells of the rabbit heart.
