Molecular aspects of adrenergic modulation of cardiac L-type Ca ²⁺ channels

L-type Ca ²⁺ channels are predominantly regulated by β-adrenergic stimulation, enhancing L-type Ca ²⁺ current by increasing the mean channel open time and/or the opening probability of functional Ca ²⁺ channels. Stimulation of β-adrenergic receptors (ARs) results in an increased cyclic adenosine monophosphate (cAMP) production by adenylate cyclase (AC) and consequently activation of protein kinase (PK) A and phosphorylation of L-type Ca ²⁺ channels by this enzyme. β ₁-Adrenergic receptors couple exclusively to the G protein Gs, producing a widespread increase in cAMP levels in the cell, whereas β ₂-adrenergic receptors couple to both Gs and Gi, producing a more localized activation of L-type Ca ²⁺ channels. Other signaling intermediates (protein kinase C, protein kinase G or protein tyrosine kinase (PTK)) either have negative effects on L-type Ca ²⁺ current, or they interact with the stimulatory effect of the protein kinase A pathway.