Heparin/heparan sulfates bind to and modulate neuronal L-type (Cav1.2) voltage-dependent Ca(2+) channels

Abstract

Our previous studies revealed that L-type voltage-dependent Ca(2+) channels (Cav1.2 L-VDCCs) are modulated by the neural extracellular matrix backbone, polyanionic glycan hyaluronic acid. Here we used isothermal titration calorimetry and screened a set of peptides derived from the extracellular domains of Cav1.2α1 to identify putative binding sites between the channel and hyaluronic acid or another class of polyanionic glycans, such as heparin/heparan sulfates. None of the tested peptides showed detectable interaction with hyaluronic acid, but two peptides derived from the first pore-forming domain of Cav1.2α1 subunit bound to heparin. At 25 °C the binding of the peptide P7 (MGKMHKTCYN) was at ~50 μM, and that of the peptide P8 (GHGRQCQNGTVCKPGWDGPKHG) was at ~21 μM. The Cav1.2α1 first pore forming segment that contained both peptides maintained a high affinity for heparin (~23 μM), integrating their enthalpic and entropic binding contributions. Interaction between heparin and recombinant as well as native full-length neuronal Cav1.2α1 channels was confirmed using the heparin-agarose pull down assay. Whole cell patch clamp recordings in HEK293 cells transfected with neuronal Cav1.2 channels revealed that enzymatic digestion of highly sulfated heparan sulfates with heparinase 1 affects neither voltage-dependence of channel activation nor the level of steady state inactivation, but did speed up channel inactivation. Treatment of hippocampal cultures with heparinase 1 reduced the firing rate and led to appearance of long-lasting bursts in the same manner as treatment with the inhibitor of L-VDCC diltiazem. Thus, heparan sulfate proteoglycans may bind to and regulate L-VDCC inactivation and network activity.

Keywords: Channel inactivation; Extracellular matrix; Heparan sulfate proteoglycans; L-type Ca(2+) channels; Neuron.