Functional interaction of syntaxin and SNAP‐25 with voltage‐sensitive L‐ and N‐type Ca2+ channels.

We have used an electrophysiological assay to investigate the functional interaction of syntaxin 1A and SNAP‐25 with the class C, L‐type, and the class B, N‐type, voltage‐sensitive calcium channels. Co‐expression of syntaxin 1A with the pore‐forming subunits of the L‐ and N‐type channels in Xenopus oocytes generates a dramatic inhibition of inward currents (>60%) and modifies the rate of inactivation (tau) and steady‐state voltage dependence of inactivation. Syntaxin 1–267, which lacks the transmembrane region (TMR), and syntaxin 2 do not modify channel properties, suggesting that the syntaxin 1A interaction site resides predominantly in the TMR. Co‐expression of SNAP‐25 significantly modifies the gating properties of L‐ and N‐type channels and displays modest inhibition of current amplitude. Syntaxin 1A and SNAP‐25 combined restore the syntaxin‐inhibited N‐type inward current but not the reduced rate of inactivation. Hence, a distinct interaction of a putative syntaxin 1A‐SNAP‐25 complex with the channel is apparent, consistent with the formation of a synaptosomal SNAP receptors (SNAREs) complex. The in vivo functional reconstitution: (i) establishes the proximity of the SNAREs to calcium channels; (ii) provides new insight into a potential regulatory role for the two SNAREs in controlling calcium influx through N‐ and L‐type channels; and (iii) may suggest a pivotal role for calcium channels in the secretion process.