Direct voltage control of endogenous lysophosphatidic acid G-protein-coupled receptors in Xenopus oocytes

Lysophosphatidic acid (LPA) G-protein-coupled receptors (GPCRs) play important roles in a variety of physiological and pathophysiological processes, including cell proliferation, angiogenesis, central nervous system development and carcinogenesis. Whilst many ion channels and transporters are recognized to be controlled by a change in cell membrane potential, little is known about the voltage dependence of other proteins involved in cell signalling. Here, we show that the InsP3-mediated Ca2+ response stimulated by the endogenous LPA GPCR in Xenopus oocytes is potentiated by membrane depolarization. Depolarization was able to repetitively stimulate transient [Ca2+]i increases after the initial agonist-evoked response. In addition, the initial rate and amplitude of the LPA-dependent Ca2+ response were significantly modulated by the steady holding potential over the physiological range, such that the response to LPA was potentiated at depolarized potentials and inhibited at hyperpolarized potentials. Enhancement of LPA receptor-evoked Ca2+ mobilization by membrane depolarization was observed over a wide range of agonist concentrations. Importantly, the amplitude of the depolarization-evoked intracellular Ca2+ increase displayed an inverse relationship with agonist concentration such that the greatest effect of voltage was observed at near-threshold levels of agonist. Voltage-dependent Ca2+ release was not induced by direct elevation of InsP3 or by activation of heterotrimeric G-proteins in the absence of agonist, indicating that the LPA GPCR itself represents the primary site of action of membrane voltage. This novel modulation of LPA signalling by membrane potential may have important consequences for control of Ca2+ signals both in excitable and non-excitable tissues

Sigma-1 Agonist Binding in the Aging Rat Brain: a MicroPET Study with [11C]SA4503

Purpose: Sigma-1 receptor ligands modulate the release of several neurotransmitters and intracellular calcium signaling. We examined the binding of a radiolabeled sigma-1 agonist in the aging rat brain with positron emission tomography (PET). Procedures: Time-dependent uptake of [11C]SA4503 was measured in the brain of young (1.5 to 3 months) and aged (18 to 32 months) Wistar Hannover rats, and tracer-kinetic models were fitted to this data, using metabolite-corrected plasma radioactivity as input function. Results: In aged animals, the injected probe was less rapidly metabolized and cleared. Logan graphical analysis and a 2-tissue compartment model (2-TCM) fit indicated changes of total distribution volume (VT) and binding potential (BPND) of the tracer. BPND was reduced particularly in the (hypo)thalamus, pons, and medulla. Conclusions: Some areas showed reductions of ligand binding with aging whereas binding in other areas (cortex) was not significantly affected. © 2015 The Author(s