Extracellular ATP is an important neurotransmitter that modulates cardiac function by activation of purinergic receptors. In this study, the effect of P2 purinergic receptor activation on contractions and on [Ca2+](i) was investigated in adult rat ventricular myocytes. Fura 2 was used to measure [Ca2+](i), and video edge detection was used to measure contraction. Superfusion of 2-methylthio-adenosine-5'-triphosphate (2-M-S-ATP) over quiescent myocytes induced oscillations in contraction and in [Ca2+](i). The frequency of the oscillatory contractions increased with increasing concentrations of 2-M-S-ATP, but the amplitude of contractions varied from cell to cell and was independent of the concentration of 2-M-S-ATP. During electrical stimulation, activation of purinergic receptors in myocytes potentiated the amplitude of contraction and induced arrhythmias. In populations of quiescent myocytes, the 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 cells. Pretreatment of quiescent myocytes with thapsigargin or caffeine reduced or abolished the oscillations in contractions and in [Ca2+](i) triggered by 2-M-S-ATP, indicating a dependence of the oscillations on uptake and release of Ca2+ by the sarcoplasmic reticulum. These data demonstrate the novel phenomenon that activation of purinergic receptors in quiescent myocytes stimulates oscillations in [Ca2+](i) and contraction. In electrically stimulated myocytes, activation of purinergic receptors triggers oscillatory contractions and potentiates the amplitude of electrically triggered contractions.
- Ca transient
- oscillatory contraction
- purinergic receptor
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine