Differential Regulation of Ca2+ Signaling and Membrane Trafficking by Multiple P2 Receptors in Brown Adipocytes

Extracellular ATP triggers changes in intracellular Ca2+, ion channel function, and membrane trafficking in adipocytes. The aim of the present study was to determine which P2 receptors might mediate the Ca2+ signaling and membrane trafficking responses to ATP in brown fat cells. RT-PCR was used to determine which P2 receptors are expressed in brown fat cells. Responses to nucleotide agonists and antagonists were characterized using fura-2 fluorescence imaging of Ca2+ responses, and FM 1-43 fluorescence imaging and membrane capacitance measurements to assess membrane trafficking. The pharmacology of the Ca2+ responses fits the properties of the P2Y receptors for which mRNA is expressed, but the agonist and antagonist sensitivity of the membrane-trafficking response was not consistent with any P2 receptor described to date. Brown adipocytes expressed mRNA for P2Y2, P2Y6, and P2Y12 metabotropic receptors and P2X1, P2X2, P2X3, P2X4, P2X5, and P2X7 ionotropic receptors. The agonists ATP, ADP, UTP, UDP and 2[variant prime], 3[variant prime]-(benzoylbenzoyl) ATP (BzATP) increased intracellular Ca2+, while 100 μM suramin, pyridoxal-phosphate-6-azophenyl-2[variant prime] 4[variant prime]-disulfonic acid (PPADS), or Reactive Blue 2 partially blocked Ca2+ responses. ATP, but not ADP, UTP, UDP or BzATP activated membrane trafficking. The membrane response could be blocked completely with 1 μM PPADS but not by the antagonist MRS2179. We conclude that multiple P2 receptors mediate the ATP responses of brown fat cells, and that membrane trafficking is regulated by a P2 receptor showing unusual properties.