Transient Receptor Potential Channel 1 (TRPC1) Reduces Calcium Permeability in Heteromeric Channel Complexes

Abstract

Specific biological roles of the classical transient receptor potential channel 1 (TRPC1) are still largely elusive. To investigate the function of TRPC1 proteins in cell physiology, we studied heterologously expressed TRPC1 channels and found that recombinant TRPC1 subunits do not form functional homomeric channels. Instead, by electrophysiological analysis TRPC1 was shown to form functional heteromeric, receptoroperated channel complexes with TRPC3, -4, -5, -6, and -7 indicating that TRPC1 proteins can co-assemble with all members of the TRPC subfamily. In all TRPC1-containing heteromers, TRPC1 subunits significantly decreased calcium permeation. The exchange of select amino acids in the putative pore-forming region of TRPC1 further reduced calcium permeability, suggesting that TRPC1 subunits contribute to the channel pore. In immortalized immature gonadotropin-releasing hormone neurons endogenously expressing TRPC1, -2, -5, and -6, down-regulation of TRPC1 resulted in increased calcium permeability and elevated basal cytosolic calcium concentrations. We did not observe any involvement of TRPC1 in storeoperated cation influx. Notably, TRPC1 suppressed the migration of gonadotropin-releasing hormone neurons without affecting cell proliferation. Conversely, in TRPC1 knockdown neurons, specific migratory properties like distance covered, locomotion speed, and directionality were increased. These findings suggest a novel regulatory mechanism relying on the expression of TRPC1 and the subsequent formation of heteromeric TRPC channel complexes with reduced calcium permeability, thereby fine-tuning neuronal migration.The classical transient receptor potential (TRPC) 2 channel subfamily comprises seven members (TRPC1-7) that are regarded as non-selective, calcium-permeable cation channels involved in a wide range of physiological events that require calcium (Ca 2ϩ ) signaling. To date, it is broadly accepted that the general activation mechanism of TRPC channels is contingent upon receptor-mediated phospholipase C activation independent of protein kinase C activity and the depletion of internal calcium stores (1). However, channel activation subsequent to store depletion is also discussed for some TRPC family members (summarized by Ref. 2). TRPC channels are widely expressed in different mammalian tissues like vascular smooth muscle, lung, kidney, and brain, and they have been identified to participate in central cell physiological processes (3). In the nervous system, for example, TRPC channels are involved in neuronal development, proliferation, and differentiation (4, 5), and a growing body of evidence indicates that TRPC channels are involved in neurological diseases (6).For TRPC1 channels, an involvement in stretch-induced (7) and in store-operated calcium (SOC) influx is discussed (8 -10). Previous investigations of TRPC1 gene-deficient mice indicated that TRPC1 was neither involved in store-operated cation influx in vascular smooth muscle cells and in platelets (11, 12) nor in pressure-induced cation influx (11...

REST levels affect the functional expression of voltage dependent calcium channels and the migratory activity in immortalized GnRH neurons

“…SM 2 shows the results of quantitative PCR analysis of the transcripts of the major classes of VDCCs: Ca V 1.2, 1.3 (L-type), 2.1 (P/Q), 2.2 (N) and 3.2 (T) channels. Interestingly, and at variance with the data reported in [22], all are expressed both in the control and in the silenced line. A threefold increase of Ca V 1.2 and a slight but significant decrease of Ca V 1.3 and Ca V 3.2 was detected in the 994-D4 line as compared to GN11 cells, while for other two channel types no significant change in the level of the transcripts could be detected.…”

“…voltage dependent channels [18,19]; more recently, however, expression of the transcript of P/Q type VDCCs has been reported [22]. For this reason, we reexamined VDCCs expression and functionality in both control and silenced cells, using a calcium imaging approach.…”

“…3F), indicative of a greater density of VDCCs. In order to identify the nature of the channels involved, we performed a set of tests with blockers of VDCCs, starting with ω-agatoxin IVA, a selective blocker of P/Q channels, whose transcripts have been reported to be present in this cell line [22]. For these experiments, we focused on GN11 and 4B, C).…”

Evidence of a Role for Fibroblast Transient Receptor Potential Canonical 3 Ca2+ Channel in Renal Fibrosis

“…Specific siRNA-mediated TRPC1 and -6 knockdown did not affect Ca 2+ entries and cell proliferation. Likewise, previous studies showed that TRPC1 did not form functional homomeric channels, 98 whereas TRPC6 was absent in fibroblasts. 87 Consequently, because TRPC3 inhibition was sufficient in blocking Ca 2+ entries, we did not further investigate the roles of these channels in renal fibroblasts function.…”

Calcium Signaling in Neuronal Motility: Pharmacological Tools for Investigating Specific Pathways

“…Ariano et al [73] analyzed the spontaneous calcium oscillations in [35]: they showed that in heterologous systems, TRPC1 assembly in heterotetramers reduced calcium permeation through the channels; in GN11 neurons, TRPC1 downregulation increased calcium permeability and migratory velocity and directionality. These discrepancies can be explained by the fact that TRPC1 channels, as stated above, form heterotetramers with the other subunits (these cells express also TRPC2, 5 and, according to [35], TRPC6): the anti-TRPC1 Ab, by interfering with this subunit, may modify the permeability of the whole assembly, thus blocking the heterotetrameric channel.…”