CaV1.1 is a slowly activating voltage-gated Ca2+ channel that exists in two splice variants with different voltage sensitivities. By making chimeras of these variants, Tuluc et al. show that activation kinetics and voltage dependence are controlled by distinct molecular mechanisms in the voltage-sensing domains of repeats I and IV, respectively.

The adaptor proteins STAC1, STAC2, and STAC3 represent a newly identified family of regulators of voltage-gated calcium channel (Ca V ) trafficking and function. The skeletal muscle isoform STAC3 is essential for excitation-contraction coupling and its mutation causes severe muscle disease. Recently, two distinct molecular domains in STAC3 were identified, necessary for its functional interaction with Ca V 1.1: the C1 domain, which recruits STAC proteins to the calcium channel complex in skeletal muscle triads, and the SH3-1 domain, involved in excitation-contraction coupling. These interaction sites are conserved in the three STAC proteins. However, the molecular domain in Ca V 1 channels interacting with the STAC C1 domain and the possible role of this interaction in neuronal Ca V 1 channels remained unknown. Using Ca V 1.2/2.1 chimeras expressed in dysgenic (Ca V 1.1) myotubes, we identified the amino acids 1,641-1,668 in the C terminus of Ca V 1.2 as necessary for association of STAC proteins. This sequence contains the IQ domain and alanine mutagenesis revealed that the amino acids important for STAC association overlap with those making contacts with the C-lobe of calcium-calmodulin (Ca/CaM) and mediating calcium-dependent inactivation of Ca V 1.2. Indeed, patch-clamp analysis demonstrated that coexpression of either one of the three STAC proteins with Ca V 1.2 opposed calcium-dependent inactivation, although to different degrees, and that substitution of the Ca V 1.2 IQ domain with that of Ca V 2.1, which does not interact with STAC, abolished this effect. These results suggest that STAC proteins associate with the Ca V 1.2 C terminus at the IQ domain and thus inhibit calcium-dependent feedback regulation of Ca V 1.2 currents.ecently STAC3 (SH3 and cysteine-rich containing protein 3) has been identified as an essential regulator of calcium channel trafficking and function in skeletal muscle excitationcontraction (EC) coupling and a mutation in STAC3 has been linked to the severe muscle disease Native American myopathy (NAM) (1, 2). Expression of STAC3 is restricted to skeletal muscle, where STAC3 associates with the voltage-gated calcium channel Ca V 1.1 and is involved in mediating voltage-induced calcium release from the sarcoplasmic reticulum (3, 4). In nonmuscle cells, STAC3 was shown to facilitate functional membrane expression of Ca V 1.1 and alter the current properties of Ca V 1.2 (5), suggesting a role of STAC proteins as an L-type calcium channel (Ca V 1) regulator. STAC3 belongs to a family of adaptor proteins that comprises two additional isoforms, STAC1 and STAC2, which are highly expressed in the brain (1).All three STAC proteins contain one C1 domain and two SH3 protein interaction domains (6). We previously demonstrated that the stable association of STAC3 to the Ca V 1 channel complex in the triads of skeletal muscle relies on the C1 domain (7). In contrast, the NAM mutation, which impairs EC coupling and is located in the SH3-1 domain of STAC3 (2-4), did not abolish the interaction with ...

Highlights d PA produced by PLD1 is involved in distinct steps of neuroendocrine exocytosis d Secretagogue-evoked stimulation leads to the production of several PA species d Mono-unsaturated PA regulates the number of exocytotic events d Poly-unsaturated PA regulates fusion pore stability and expansion