RESUMO
RATIONALE: It is unknown whether every ventricular myocyte expresses all 5 of the cardiac adrenergic receptors (ARs), ß1, ß2, ß3, α1A, and α1B. The ß1 and ß2 are thought to be the dominant myocyte ARs. OBJECTIVE: Quantify the 5 cardiac ARs in individual ventricular myocytes. METHODS AND RESULTS: We studied ventricular myocytes from wild-type mice, mice with α1A and α1B knockin reporters, and ß1 and ß2 knockout mice. Using individual isolated cells, we measured knockin reporters, mRNAs, signaling (phosphorylation of extracellular signal-regulated kinase and phospholamban), and contraction. We found that the ß1 and α1B were present in all myocytes. The α1A was present in 60%, with high levels in 20%. The ß2 and ß3 were detected in only ≈5% of myocytes, mostly in different cells. In intact heart, 30% of total ß-ARs were ß2 and 20% were ß3, both mainly in nonmyocytes. CONCLUSION: The dominant ventricular myocyte ARs present in all cells are the ß1 and α1B. The ß2 and ß3 are mostly absent in myocytes but are abundant in nonmyocytes. The α1A is in just over half of cells, but only 20% have high levels. Four distinct myocyte AR phenotypes are defined: 30% of cells with ß1 and α1B only; 60% that also have the α1A; and 5% each that also have the ß2 or ß3. The results raise cautions in experimental design, such as receptor overexpression in myocytes that do not express the AR normally. The data suggest new paradigms in cardiac adrenergic signaling mechanisms.
