Cross‐regulation between β 1 ‐ and β 3 ‐adrenoceptors following chronic β‐adrenergic stimulation in neonatal rat cardiomyocytes

Background and purpose:  We have previously shown that β‐adrenoceptors continuously stimulated with noradrenaline induces an increase in β 3 ‐adrenoceptors (Gα i PCRs) and a decrease in β 1 ‐adrenoceptors (Gα s PCRs) at functional, genomic and protein levels. This compensatory modification induced by noradrenaline is probably one of the consequences of cardiac depression observed in heart disease. Therefore, we investigated further the interaction between β 1 ‐ and β 3 ‐adrenoceptors in neonatal rat cardiomyocytes. Experimental approach:  Functional studies were performed by cyclic adenosine monophosphate (cAMP) accumulation assays in cells untreated or treated with dobutamine and ICI 118551 (β 1 ‐adrenoceptor) or CL‐3162436243 (β 3 ‐adrenoceptor) for 24 h in the presence or absence of protein kinase inhibitors. β‐adrenoceptor and protein kinase expression was monitored by quantitative reverse transcription‐polymerase chain reaction (RT‐PCR) and by Western blotting, respectively. Key results:  Chronic β 1 ‐ or β 3 ‐adrenoceptor stimulation reduced β 1 ‐adrenoceptor‐mediated cAMP accumulation in association with a decrease in β 1 ‐adrenoceptor mRNA and protein levels through protein kinase C (PKC), phosphoinositide 3‐kinase (PI3K) and p38 mitogen‐activated protein kinase (p38MAPK) activation. In contrast, both treatments induced an increase in β 3 ‐adrenoceptor expression and β 3 ‐adrenoceptor‐inhibited forskolin response through PKC, extracellular‐signal‐regulated kinases 1 and 2 (ERK1/2) and p38MAPK phosphorylation, although no β 3 ‐adrenoceptor response was observed in untreated cells. ERK1/2 and p38MAPK were activated by both treatments. The modulation of β 1 ‐ or β 3 ‐adrenoceptor function did not require stress‐activated protein kinase/c‐Jun N‐terminal kinase (SAPK/JNK) although chronic β 1 ‐adrenoceptor stimulation activated SAPK/JNK. β 3 ‐adrenoceptor treatment activated Akt although PI3K was not involved in β 3 ‐adrenoceptor up‐regulation. Conclusion and implications:  We show for the first time that chronic β 1 ‐ or β 3 ‐adrenoceptor stimulation leads to the modulation of β 1 ‐ and β 3 ‐adrenoceptors by a cross‐regulation involving PKC, PI3K p38MAPK and MEK/ERK1/2 pathway, and through protein kinase A when β 1 ‐adrenoceptors are chronically activated.