Graded Ca2+/calmodulin-dependent coupling of voltage-gated CaV1.2 channels

Abstract

In the heart, reliable activation of Ca2+ release from the sarcoplasmic reticulum during the plateau of the ventricular action potential requires synchronous opening of multiple CaV1.2 channels. Yet the mechanisms that coordinate this simultaneous opening during every heartbeat are unclear. Here, we demonstrate that CaV1.2 channels form clusters that undergo dynamic, reciprocal, allosteric interactions. This ‘functional coupling’ facilitates Ca2+ influx by increasing activation of adjoined channels and occurs through C-terminal-to-C-terminal interactions. These interactions are initiated by binding of incoming Ca2+ to calmodulin (CaM) and proceed through Ca2+/CaM binding to the CaV1.2 pre-IQ domain. Coupling fades as [Ca2+]i decreases, but persists longer than the current that evoked it, providing evidence for ‘molecular memory’. Our findings suggest a model for CaV1.2 channel gating and Ca2+-influx amplification that unifies diverse observations about Ca2+ signaling in the heart, and challenges the long-held view that voltage-gated channels open and close independently.DOI: http://dx.doi.org/10.7554/eLife.05608.001

Oxidative stress decreases microtubule growth and stability in ventricular myocytes

“…Super-resolution imaging was performed as described previously [36, 37]. Briefly, cardiomyocytes were fixed by incubating in 4% paraformaldehyde in PBS at 37 °C for 30 m, then washed with PBS and blocked for 1 h at room temperature in 50% SEA BLOCK (Thermo Fisher Scientific Waltham, MA) and 0.5% w/v Triton X-100 in PBS (blocking buffer).…”

Surface dynamics of voltage-gated ion channels

“…In most models, the positioning of calcium channels has been assumed to be fixed in place to maximize the signaling capacity of local intracellular calcium domains of opened channels without crosstalk to neighboring entry sites, 101,129 but there is an accumulating body of evidence to suggest otherwise. 41,123 In addition, the fast action of intracellular calcium buffers and calcium-binding proteins support this picture. 49,129 Changes in the conductivity, steady-state inactivation by the interaction with SNARE proteins such as syntaxin and SNAP 25, 14,15 as well as calmodulin mediated calcium-dependent inactivation/facilitation 30,99 are considered as the self-possessed properties of the channel that determine its signaling capacity.…”

“…) positive cooperativity of Ca V 1.2 channels. 41 Whether dynamic binding and unbinding from identified scaffold protein can induce similar cooperativity, for instance in the active zone of the presynaptic membrane or complexes with BK Ca channels, requires further investigation.…”

“…In particular, the development of high-resolution imaging techniques demonstrated that dynamic activity-dependent redistribution of ionotropic receptors in the synaptic membrane as a complementary mechanism of shortterm synaptic plasticity 9,33,65,111 might also be relevant for voltage-gated ion channels. 41,119 Aspects of surface dynamics Molecular dynamics of ion channels has been related to either the structural dynamics of the pore-forming subunit, allowing the passage of ions through the membrane, 11 or to lateral diffusion in the cellular membrane caused by its sub-cellular heterogeneity. 102,112 The need of molecular motions for the opening and closing of ion channels is well defined and is in the range of a few Angstroms (or several hundred picometers).…”

“…A striking example for such local transient interaction has been shown for calcium channels in cardiac myocytes, where clustered organization of Ca V 1.2 determines the size of the intracellular calcium domain and is essential for the excitation-contraction coupling. As demonstrated by Dixon et al (2015), transient interactions of Ca V 1.2 channels with each other via the C-terminus, which lead to positive cooperativity at opening, depends on, but persists longer than, the initial calcium influx and may reflect a kind of "molecular memory" imprinted in the local organization of calcium channels. 41,42 Thus, the dynamic organization of ion channel clusters along the neuronal membrane might indeed serve as a readout for such molecular memory traces that carry the potential to trigger long-lasting changes in neuronal excitability.…”