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How adrenaline activates Cav1.2
The L-type Ca2+ channel Cav1.2 controls heart rate and neuronal excitability. Qian et al. found that enhancement of Cav1.2 channel activity in the brain by β-adrenergic receptor (βAR) signaling required phosphorylation of Ser1928, whereas in the heart, this site was dispensable for βAR-mediated regulation. In contrast to those from wild-type mice, hippocampal neurons from mice, in which Ser1928 of Cav1.2 was mutated to alanine, did not exhibit increased L-type calcium channel activity in response to β-adrenergic stimulation. Phosphorylation of Ser1928 involved signaling through the β2AR, but not through the β1AR, and this phosphorylation event enabled a particular form of long-term potentiation, a process linked to learning and memory. These results were in marked contrast to βAR-mediated regulation of Cav1.2 activity in cardiomyocytes, which involved β1AR and was independent of Ser1928. This differential regulation in the heart and brain implies that tissue-specific therapeutics could be identified.
Abstract
The L-type Ca2+ channel Cav1.2 controls multiple functions throughout the body including heart rate and neuronal excitability. It is a key mediator of fight-or-flight stress responses triggered by a signaling pathway involving β-adrenergic receptors (βARs), cyclic adenosine monophosphate (cAMP), and protein kinase A (PKA). PKA readily phosphorylates Ser1928 in Cav1.2 in vitro and in vivo, including in rodents and humans. However, S1928A knock-in (KI) mice have normal PKA-mediated L-type channel regulation in the heart, indicating that Ser1928 is not required for regulation of cardiac Cav1.2 by PKA in this tissue. We report that augmentation of L-type currents by PKA in neurons was absent in S1928A KI mice. Furthermore, S1928A KI mice failed to induce long-term potentiation in response to prolonged theta-tetanus (PTT-LTP), a form of synaptic plasticity that requires Cav1.2 and enhancement of its activity by the β2-adrenergic receptor (β2AR)–cAMP–PKA cascade. Thus, there is an unexpected dichotomy in the control of Cav1.2 by PKA in cardiomyocytes and hippocampal neurons.
