β-Adrenergic subtypes in chick embryonic cardiac myocytes

Four beta-AR subtypes are thought to exist in the heart of many species, including human heart. The aim of this study is to confirm the presence of the four beta-AR subtypes in chick embryo ventricular cardiomyocytes. Various agents acting on specific beta-ARs were added to the cells, and changes in the spontaneous contraction rate recorded (bpm). Isoprenaline (ISO) and propranolol were used as high affinity beta 1 (beta 1(II))/beta 2 agonist and antagonist, respectively. In addition, BRL37344 and CGP12177 were used to stimulate beta 3-ARs and the low affinity beta 1 (beta 1(L))-ARs, respectively. The addition of 100 nM ISO led to an increase in the contraction rate by approximately 21%, from 56 +/- 2.81 bpm to 73 +/- 4.09 bpm. Subsequent addition of 200 nM propranolol reduced the contraction rate by approximately 34%, from 73 +/- 4.09 bpm to 48 +/- 3.82 bpm. A further reduction in the contraction rate was observed with 600 nM BRL37344 (48 +/- 3.82 bpm to 40 +/- 1.84 bpm). Lastly, the addition of 1 mu M CGP12177 in the presence of 200 nM propranolol resulted in an increase in contraction rate from 40 +/- 1.84 bpm to 55 +/- 4.30 bpm. The results obtained in this study confirm the presence of four distinct beta-AR subtypes within ventricular cells of the chick embryo cardiomyocytes.