title: Membrane potential regulates nicotinic acid adenine dinucleotide phosphate (NAADP) dependence of the pH- and Ca2+-sensitive organellar two-pore channel TPC1.
abstract: Nicotinic acid adenine dinucleotide phosphate (NAADP) is a potent second messenger that mobilizes Ca(2+) from the acidic endolysosomes by activation of the two-pore channels TPC1 and TPC2. The channel properties of human TPC1 have not been studied before, and its cellular function is not known. In the present study, we characterized TPC1 incorporated into lipid bilayers. The native and recombinant TPC1 channels are activated by NAADP. TPC1 activity requires acidic luminal pH and high luminal Ca(2+). With Ba(2+) as the permeable ion, luminal Ca(2+) activates TPC1 with an apparent K(m) of 180 μm. TPC1 operates in two tightly coupled conductance states of 47 ± 8 and 200 ± 9 picosiemens. Importantly, opening of the large conductance markedly increases the small conductance mean open time. Changes in membrane potential from 0 to -60 mV increased linearly both the small and the large conductances and NP(o), indicating that TPC1 is regulated by voltage. Intriguingly, the apparent affinity for activation of TPC1 by its ligand NAADP is not constant. Rather, hyperpolarization increases the apparent affinity of TPC1 for NAADP by 10 nm/mV. The concerted regulation of TPC1 activity by luminal Ca(2+) and by membrane potential thus provides a potential mechanism to explain NAADP-induced Ca(2+) oscillations. These findings reveal unique properties of TPC1 to explain its role in Ca(2+) oscillations and cell function.
authors.affiliation: Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, NIDCR, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Volodymyr
authors.initials: V
authors.lastname: Rybalchenko
authors.forename: Malini
authors.initials: M
authors.lastname: Ahuja
authors.forename: Jessica
authors.initials: J
authors.lastname: Coblentz
authors.forename: Dev
authors.initials: D
authors.lastname: Churamani
authors.forename: Sandip
authors.initials: S
authors.lastname: Patel
authors.forename: Krill
authors.initials: K
authors.lastname: Kiselyov
authors.forename: Shmuel
authors.initials: S
authors.lastname: Muallem
mesh_terms: D001683:Biological Clocks / Q000502:physiology*; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D015220:Calcium Channels / Q000737:chemistry / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology*; D009249:NADP / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D000097903:Two-Pore Channels
chemical_list: D002118:Calcium; D015220:Calcium Channels; D008051:Lipid Bilayers; D009249:NADP; C407357:TPCN1 protein, human; D000097903:Two-Pore Channels; C530224:TPCN2 protein, human; C024376:NAADP