L-type Ca 2+ channels are predominantly regulated by h-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 h-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. h 1 -Adrenergic receptors

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... e exclusively to the G protein Gs, producing a widespread increase in cAMP levels in the cell, whereas h 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.