ACTIVATION OF PURINERGIC RECEPTORS TRIGGERS OSCILLATORY CONTRACTIONS IN ADULT-RAT VENTRICULAR MYOCYTES

Extracellular ATP is an important neurotransmitter that modulates card iac function by activation of purinergic receptors. In this study, the effect of P-2 purinergic receptor activation on contractions and on [ Ca2+](i) was investigated in adult rat ventricular myocytes. Fura 2 wa s used to measure [Ca2+](i), and video edge detection was used to meas ure contraction. Superfusion of 2-methylthio-adenosine-5'-triphosphate (2-M-S-ATP) over quiescent myocytes induced oscillations in contracti on and in [Ca2+](i). The frequency of the oscillatory contractions inc reased with increasing concentrations of 2-M-S-ATP, but tile amplitude of contractions varied from cell to cell and was independent of the c oncentration of 2-M-S-ATP. During electrical stimulation, activation o f purinergic receptors In myocytes potentiated the amplitude of contra ction and induced arrhythmias. In populations of quiescent myocytes, t he plateau phase of the [Ca2+](i) signal evoked by 2-M-S-ATP could be shown to represent summed oscillations in [Ca2+](i) in individual cell s. Pretreatment of quiescent myocytes with thapsigargin or caffeine re duced or abolished the oscillations in contractions and in [Ca2+](i) t riggered by 2-M-S-ATP, indicating a dependence of the oscillations on uptake and release of Ca2+ by the sarcoplasmic reticulum. These data d emonstrate the novel phenomenon that activation of purinergic receptor s in quiescent myocytes stimulates oscillations in [Ca2+](i) and contr action. In electrically stimulated myocytes, activation of purinergic receptors triggers oscillatory contractions and potentiates the amplit ude of electrically triggered contractions.