Adenosine A2A and β-adrenergic calcium transient and contractile responses in rat ventricular myocytes

The adenosine A2A receptor (A2AR) enhances cardiac contractility, and the adenosine A1R receptor (A1R) is antiadrenergic by reducing the adrenergic β1 receptor (β1R)-elicited increase in contractility. In this study we compared the A2AR-, A1R-, and β1R-elicited actions on isolated rat ventricular myocytes in terms of Ca transient and contractile responses involving PKA and PKC. Stimulation of A2AR with 2 μM (∼EC50) CGS-21680 (CGS) produced a 17–28% increase in the Ca transient ratio (CTR) and maximum velocities (Vmax) of transient ratio increase (+MVT) and recovery (−MVT) but no change in the time-to-50% recovery (TTR). CGS increased myocyte sarcomere shortening (MSS) and the maximum velocities of shortening (+MVS) and relaxation (−MVS) by 31–34% with no change in time-to-50% relengthening (TTL). β1R stimulation using 2 nM (∼EC50) isoproterenol (Iso) increased CTR, +MVT, and −MVT by 67–162% and decreased TTR by 43%. Iso increased MSS, +MVS, and −MVS by 153–174% and decreased TTL by 31%. The A2AR and β1R C...