Abstract
Adenosine A2A receptor (A2AR) activation promotes spontaneous calcium release from the sarcoplasmic reticulum (SR), which can potentially destabilize the beat-to-beat response. To test if A2AR activation alters beat-to-beat stability, patch-clamp technique was used in isolated human atrial myocytes to measure beat-to-beat changes in L-type calcium current and the tail current elicited upon repolarization. Calcium imaging was used to measure the calcium transient and its propagation in multicellular atrial HL-1 myocyte preparations. The stimulation frequency was increased stepwise (from 0.2 to 2Hz) and beat-to-beat responses were determined at each frequency, and were classified as uniform alternating or irregular. In human atrial myocytes, 200 nM of the A2AR agonist CGS21680 decreased the fraction of uniform responses at 1 Hz (from 23/36 to 15/36) and reduced the maximal frequency where a uniform response could be maintained (from 1.11±0.10 to 0.80±0.08 Hz, p<0.05). The frequency dependent reduction of uniform responses in the presence of CGS21680 was due to the concurrent increase in fraction of irregular responses (from 1/36 to 7/36 at 1 Hz and from 13/36 to 26/36 at 2 Hz). In cultured atrial HL-1 myocytes, CGS21680 also decreased the number of uniform responses from 50/80 to 35/80. Moreover, CGS21680 destabilized the propagation of the calcium transient. Overall, a uniform propagation of 38/80 calcium transients was observed in control conditions and only 22/80 transients showed uniform propagation after exposure to CGS21680. We conclude that stimulation of adenosine A2A receptors promotes the induction of irregular beat-to-beat responses at lower stimulation frequencies and favors a non-uniform propagation of the calcium transient, which may contribute to the generation of atrial arrhythmia.
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