Phosphorylation of Ca _v 1.2 on S1928 uncouples the L‐type Ca ²⁺ channel from the β ₂ adrenergic receptor

Abstract

Agonist-triggered downregulation of b-adrenergic receptors (ARs) constitutes vital negative feedback to prevent cellular overexcitation. Here, we report a novel downregulation of b 2 AR signaling highly specific for Ca v 1.2. We find that b 2 -AR binding to Ca v 1.2 residues 1923-1942 is required for b-adrenergic regulation of Ca v 1.2. Despite the prominence of PKA-mediated phosphorylation of Ca v 1.2 S1928 within the newly identified b 2 AR binding site, its physiological function has so far escaped identification. We show that phosphorylation of S1928 displaces the b 2 AR from Ca v 1.2 upon b-adrenergic stimulation rendering Ca v 1.2 refractory for several minutes from further b-adrenergic stimulation. This effect is lost in S1928A knock-in mice. Although AMPARs are clustered at postsynaptic sites like Ca v 1.2, b 2 AR association with and regulation of AMPARs do not show such dissociation. Accordingly, displacement of the b 2 AR from Ca v 1.2 is a uniquely specific desensitization mechanism of Ca v 1.2 regulation by highly localized b 2 AR/cAMP/PKA/ S1928 signaling. The physiological implications of this mechanism are underscored by our finding that LTP induced by prolonged theta tetanus (PTT-LTP) depends on Ca v 1.2 and its regulation by channel-associated b 2 AR.

The Role of Reactive Oxygen Species in β-Adrenergic Signaling in Cardiomyocytes from Mice with the Metabolic Syndrome

“…The ISO-induced increase in L-type Ca 2+ current was blocked by NAC in control cardiomyocytes (Fig 3 D ), but not in HFD and ob/ob cardiomyocytes (Fig 3 E and 3 F ). The β-adrenergic-induced L-type Ca 2+ channel activation involves cAMP-PKA-dependent phosphorylation of the channel [42, 43]. Thus, the present results indicate that this signaling includes a ROS-dependent component in WT cardiomyocytes, which agrees with previous results from our group [11], whereas the signaling is ROS-independent in HFD and ob / ob cardiomyocytes.…”

Phosphorylation of Ser 1928 mediates the enhanced activity of the L-type Ca 2+ channel Ca v 1.2 by the β 2 -adrenergic receptor in neurons

“…A second application of the βAR agonist ISO only increases L-type currents in neurons if added more than 5 min after the first application has ended (17). In neuronal cultures from the hippocampal CA1, CA2, and CA3 regions, augmentation of L-type currents by ISO is much more apparent in cell-attached recordings, which typically yield increases of >200% (17, 25, 27), than in whole-cell recordings, which only show increases of 10 to 20% (27, 28). The weak ISO effect in whole-cell recordings from neurons is much smaller than in whole-cell recordings from cardiomyocytes (43).…”

“…To functionally test whether Ser 1928 phosphorylation mediates this refractory period of L-type current augmentation, we recorded single-channel L-type currents from hippocampal neurons cultured from wild-type and S1928A KI mice by cell-attached patch-clamping (Fig. 1A), using conditions as previously described (17, 25). …”

“…LTP is a key cellular correlate of learning and memory. In particular, L-type Ca 2+ currents conducted by the voltage-gated calcium channel Ca v 1.2 are important for LTP induced by the widely used 1-s-long, 200-Hz tetanus (15, 16) or by a 90- to 180-s-long, 5- to 10-Hz tetanus mimicking the endogenous ~7-Hz theta rhythm, which we call prolonged theta-tetanus LTP (PTT-LTP) (17). Ca 2+ influx through Ca v 1.2 is also important for long-term depression (LTD) induced by metabotropic glutamate receptor (mGluR) signaling (18).…”

“…This complex allows highly localized and thereby effective and specific signaling from the β 2 AR to Ca v 1.2 in neurons (25) and cardiomyocytes (29, 48) [for a review, see (24)]. The β 2 AR binds to α 1 1.2 residues 1923 to 1942, and this interaction is strictly required for receptor-mediated regulation of Ca v 1.2 (17). Furthermore, stimulating the β 2 AR leads to its temporary displacement from Ca v 1.2, creating a refractory period of ~5 min, during which neither phosphorylation nor channel activity of Ca v 1.2 can be augmented again by restimulation of the β 2 AR (17).…”