Dopamine increases L-type calcium current more in newborn than adult rabbit cardiomyocytes via D1 and beta2 receptors.

Dopamine is used to treat heart failure, particularly after cardiac surgery in infants, but the mechanisms of action are unclear. We investigated differences in the effect of dopamine on L-type calcium current (I-Ca) between newborn (NB, 1-4 days) and adult (AD, 3-4 mo) rabbit ventricular myocytes. Myocytes were enzymatically dissociated from NB and AD rabbit hearts. I-Ca was recorded by using the whole cell patch-clamp technique. mRNA levels of cardiac dopamine receptor type 1 (D1), type 2 (D2), and beta-adrenergic receptors (beta-ARs) were measured by real-time RT-PCR. Dopamine (100 mu M) increased I-Ca more in NB (E-max 87 +/- 10%) than in AD ventricular cells (E-max 21 +/- 3%). Further investigation of this difference showed that mRNA levels of the D1 receptor were significantly higher in NB, and, with beta-AR blockade, dopamine increased I-Ca more in NB than AD cells. Additionally, SKF-38393 (selective D1 receptor agonist) significantly increased I-Ca by 55 +/- 4% in NB (P < 0.05, n = 4) and by 11 +/- 1% in AD (P < 0.05, n = 6). Dopamine in the presence of SCH-23390 (D1 receptor antagonist) increased I-Ca in NB cells by 67 +/- 5% and by 22 +/- 2% in AD cells, suggesting a role for beta-AR stimulation. Selective blockade of beta(1)- or beta(2)-receptors (with block of D1 receptors) showed that the beta-AR action of dopamine in the NB was largely mediated via beta(2)-AR activation. Dopamine produces a larger increase in I-Ca in NB cardiomyocytes compared with ADs. The mechanism of action is not only through beta(2)-ARs but also due to higher expression of cardiac D1 receptor in NB.