title: PIP2 in pancreatic β-cells regulates voltage-gated calcium channels by a voltage-independent pathway.
abstract: Phosphatidylinositol-4,5-bisphosphate (PIP2) is a membrane phosphoinositide that regulates the activity of many ion channels. Influx of calcium primarily through voltage-gated calcium (CaV) channels promotes insulin secretion in pancreatic β-cells. However, whether CaVchannels are regulated by PIP2, as is the case for some non-insulin-secreting cells, is unknown. The purpose of this study was to investigate whether CaVchannels are regulated by PIP2depletion in pancreatic β-cells through activation of a muscarinic pathway induced by oxotremorine methiodide (Oxo-M). CaVchannel currents were recorded by the patch-clamp technique. The CaVcurrent amplitude was reduced by activation of the muscarinic receptor 1 (M1R) in the absence of kinetic changes. The Oxo-M-induced inhibition exhibited the hallmarks of voltage-independent regulation and did not involve PKC activation. A small fraction of the Oxo-M-induced CaVinhibition was diminished by a high concentration of Ca2+chelator, whereas ≥50% of this inhibition was prevented by diC8-PIP2dialysis. Localization of PIP2in the plasma membrane was examined by transfecting INS-1 cells with PH-PLCδ1, which revealed a close temporal association between PIP2hydrolysis and CaVchannel inhibition. Furthermore, the depletion of PIP2by a voltage-sensitive phosphatase reduced CaVcurrents in a way similar to that observed following M1R activation. These results indicate that activation of the M1R pathway inhibits the CaVchannel via PIP2depletion by a Ca2+-dependent mechanism in pancreatic β- and INS-1 cells and thereby support the hypothesis that membrane phospholipids regulate ion channel activity by interacting with ion channels.
authors.affiliation: Department of Physiology, School of Medicine, Universidad Nacional Autónoma de México (UNAM), Mexico, México.
authors.forename: Lizbeth
authors.initials: L
authors.lastname: de la Cruz
authors.affiliation: Department of Physiology, School of Medicine, Universidad Nacional Autónoma de México (UNAM), Mexico, México.
authors.forename: Erika I
authors.initials: EI
authors.lastname: Puente
authors.affiliation: Department of Physiology, School of Medicine, Universidad Nacional Autónoma de México (UNAM), Mexico, México.
authors.forename: Arturo
authors.initials: A
authors.lastname: Reyes-Vaca
authors.affiliation: Department of Physiology, School of Medicine, Universidad Nacional Autónoma de México (UNAM), Mexico, México.
authors.forename: Isabel
authors.initials: I
authors.lastname: Arenas
authors.affiliation: Department of Physiology, School of Medicine, Universidad Nacional Autónoma de México (UNAM), Mexico, México.
authors.forename: Julieta
authors.initials: J
authors.lastname: Garduño
authors.affiliation: Department of Physiology, School of Medicine, Universidad Nacional Autónoma de México (UNAM), Mexico, México.
authors.forename: Jorge
authors.initials: J
authors.lastname: Bravo-Martínez
authors.affiliation: Department of Physiology, School of Medicine, Universidad Nacional Autónoma de México (UNAM), Mexico, México erasmo@unam.mx.
authors.forename: David E
authors.initials: DE
authors.lastname: Garcia
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D020864:Calcium Channels, N-Type / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D007328:Insulin / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D008297:Male; D018408:Patch-Clamp Techniques / Q000379:methods; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011976:Receptors, Muscarinic / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D000099182:Phosphoinositide 5-Phosphatases
chemical_list: D002118:Calcium; D020864:Calcium Channels, N-Type; D007328:Insulin; D010744:Phosphoric Monoester Hydrolases; D011976:Receptors, Muscarinic; D000099182:Phosphoinositide 5-Phosphatases
keywords: PIP2; pancreatic β-cells; voltage-dependent calcium channels; voltage-independent regulation