Inhibition of TRPC5 channels by Ca2+-binding protein 1 in Xenopus oocytes

Abstract

The transient receptor potential canonical type 5 (TRPC5) channel is a member of the channels that has been implicated in neurite extension and growth cone morphology of hippocampal neurons. Although homomeric TRPC5 channels are activated following stimulation of G(q/11)-coupled receptors, the exact mechanism for this activation remains unresolved. Using two-electrode voltage clamp recordings, we show that the activity of TRPC5 channels expressed in Xenopus oocytes is dependent on the presence of Ca2+ at the extracellular as well as the cytoplasmic side of the plasma membrane. TRPC5 was activated by the stimulation of coexpressed M5 muscarinic receptors or by ionomycin. The TRPC5 activity was detectable with the presence of submillimolar levels of extracellular Ca2+, but it was eliminated by the injection of 5 mM 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid into the oocytes. Lanthanum could substitute for extracellular Ca2+ to support TRPC5 activity. Coexpression of Ca2+-binding protein 1 (CaBP1), but not calmodulin (CaM), inhibited the TRPC5 activity, without affecting the cell surface expression of TRPC5 proteins. Using in vitro binding assays, we demonstrated direction interactions between CaBP1 and TRPC5. The CaBP1-binding sites at the C terminus of TRPC5 are closely localized, but not identical, to CaM-binding sites. We conclude that TRPC5 is a Ca2+-regulated channel, and its activity is negatively controlled by CaBP1.

Critical roles of Gi/oproteins and phospholipase C-δ1 in the activation of receptor-operated TRPC4 channels

“…Incidentally, the CIRB site is also critical for the Gα i/o effect on TRPC4 (3). Moreover, Ca 2+ exhibits both positive and negative effects on some TRPC channels (20,(24)(25)(26)(27)(28).…”

“…Therefore, in addition to supporting TRPC4 function, PIP 2 also exerts a tonic inhibition on the channel. (21,(24)(25)(26)(27)(28)32). To determine if IP 3 Rs are involved in TRPC4 activation, we applied the IP 3 R inhibitor heparin (3 mg/mL) by intracellular dialysis and found that most cells failed to respond to DAMGO and subsequent application of CCh (Fig.…”

Phosphorylation of the Ca2+-Binding Protein CaBP4 by Protein Kinase C ζ in Photoreceptors

“…CaBPs bind to and yet differentially modulate a number of CaM targets, including voltage-gated Ca 2ϩ channels (Lee et al, 2002;Zhou et al, 2004;Yang et al, 2006), transient receptor potential TRP channels (Kinoshita-Kawada et al, 2005), and inositol 1,4,5-trisphosphate (IP 3 ) receptors (Yang et al, 2002;Haynes et al, 2004;Kasri et al, 2004). Through interactions with these and potentially other effectors, CaBPs may enhance the Ca 2ϩ signaling potential in neurons and other excitable cells.…”

Ca 2+ -binding protein 2 inhibits Ca 2+ -channel inactivation in mouse inner hair cells

“…CaBPs are calmodulin-like proteins that use three functional out of four helix-loop-helix domains (EF-hand) for Ca 2+ binding (27). They are thought to function primarily as signaling proteins (28) and differentially modulate calmodulin effectors (29,30). In addition, CaBPs might also contribute in buffering free cytosoloic Ca 2+ ions, as do other small EF-hand calcium-binding proteins, such as calretinin, calbindin-D-28k, and parvalbumin-α (31-33).…”