Selective stimulation of ₂ adrenergic receptors (ARs) in newborn rabbit ventricular myocardium invokes a positive inotropic effect that is lost during postnatal maturation. The underlying mechanisms for this age-related stimulatory response remain unresolved. We examined effects of ₂AR stimulation on L-type calcium current (I_Ca,L) during postnatal development. I_Ca,L was measured (37°C; either Ca²⁺ or Ba²⁺ as the charge carrier) using the whole-cell patch-clamp technique in newborn (1 to 5 days old) and adult rabbit ventricular myocytes. Ca²⁺ transients were measured concomitantly by dialyzing the cell with indo-1. Activation of ₂ARs (with either 100nM zinterol or 1µM isoproterenol in the presence of the ₁AR antagonist, CGP20712A) stimulated I_Ca,L two-fold in newborns but not in adults. The ₂AR-mediated increase in Ca²⁺ transient amplitude in newborns was due exclusively to the augmentation of I_Ca,L. Zinterol increased the rate of inactivation of I_Ca,L and increased the calcium flux integral. The ₂AR inverse agonist, ICI 118,551 (500nM), but not the ₁AR antagonist, CGP20712A (500nM), blocked the response to zinterol. Unexpectedly, the PKA blockers, H-89 (10µM), PKI 6-22 amide (10µM) and Rp-cAMP (100µM) all failed to prevent the response to zinterol, but completely blocked responses to selective ₁AR stimulation of I_Ca,L in newborns. Our results demonstrate that in addition to the conventional ₁AR-cAMP-PKA pathway, newborn rabbit myocardium exhibits a novel ₂AR-mediated, PKA-insensitive pathway that stimulates I_Ca,L. This striking developmental difference plays a major role in the age-related differences in inotropic responses to ₂AR agonists.