Caffeine- and Ryanodine-sensitive CaZ+-induced Ca 2+ Release from the Endoplasmic Reticulum in Honeybee Photoreceptors
نویسنده
چکیده
Light stimulation of invertebrate microvillar photoreceptors causes a large rapid elevation in Cai, shown previously to modulate the adaptat ional state of the cells. Cai rises, at least in part, as a result of Ins(1,4,5)Ps-induced Ca 2+ release from the submicrovillar endoplasmic reticulum (ER). Here, we provide evidence for Ca2+-induced Ca 2+ release (CICR) in an insect photoreceptor . In situ microphotometric measurements of Ca 2+ fluxes across the ER membrane in permeabil ized slices of drone bee retina show that (a) caffeine induces Ca 2+ release from the ER; (b) caffeine and Ins(1,4,5)Pa open distinct Ca ~+ release pathways because only caffeine-induced Ca 2+ release is ryanodine sensitive and heparin insensitive, and because caffeine and Ins(1,4,5)Ps have additive effects on the rate of Ca 2+ release; (c) Ca 2+ itself stimulates release of Ca 2+ via a ryanodinesensitive pathway; and (d) cADPR is ineffective in releasing Ca 2+. Microfluorometric intracellular Ca 2+ measurements with fluo-3 indicate that caffeine induces a persistent elevation in Cai. Electrophysiological recordings demonstrate that caffeine mimics all aspects of CaZ+-mediated facilitation and adaptat ion in drone photoreceptors. We conclude that the ER in drone photoreceptors contains, in addit ion to the Ins(1,4,5)Ps-sensitive release pathway, a CICR pathway that meets key pharmacological criteria for a ryanodine receptor. Coexpression of both release mechanisms could be required for the production of rapid light-induced Ca z+ elevations, because Ca 2§ amplifies its own release through both pathways by a positive feedback. CICR may also mediate the spatial spread of Ca 2+ release from the submicrovillar ER toward more remote ER subregions, thereby activating Ca z+sensitive cell processes that are not directly involved in phototransduction. I N T R O D U C T I O N Light s t imulat ion of inver tebra te microvil lar pho to recep to r s causes a large r ap id increase in the concent ra t ion o f cytosolic free calcium (Cai) (Brown and Blinks, 1974; Address correspondence to Dr. Bernd Walz, lnstitut fOr Zoophysiologie und Zellbiologie, Universit~it Potsdam, Lennestral3e 7a, D-14471 Potsdam, Germany. J. GEN. PHYSIOL. 9 The Rockefeller University Press 9 0022-1295/95/04/0537/31 $2.00 Volume 105 April 1995 537-567 537 on F ebuary 1, 2013 jgp.rress.org D ow nladed fom Published April 1, 1995
منابع مشابه
Caffeine- and ryanodine-sensitive Ca(2+)-induced Ca2+ release from the endoplasmic reticulum in honeybee photoreceptors
Light stimulation of invertebrate microvillar photoreceptors causes a large rapid elevation in Cai, shown previously to modulate the adaptational state of the cells. Cai rises, at least in part, as a result of Ins(1,4,5)P3-induced Ca2+ release from the submicrovillar endoplasmic reticulum (ER). Here, we provide evidence for Ca(2+)-induced Ca2+ release (CICR) in an insect photoreceptor. In situ ...
متن کاملCaffeine-stimulated GTH-II release involves Ca(2+) stores with novel properties.
Modulation of Ca(2+) stores with 10 mM caffeine stimulates robust secretion of gonadotropin (GTH-II) from goldfish gonadotropes. Although both endogenous forms of gonadotropin-releasing hormone (GnRH) utilize a common intracellular Ca(2+) store, sGnRH, but not cGnRH-II, uses an additional caffeine-sensitive mechanism. We examined caffeine signaling by using Ca(2+) imaging, electrophysiology, an...
متن کاملTemporal switching and cell-to-cell variability in Ca2+ release activity in mammalian cells
Genetically identical cells in a uniform external environment can exhibit different phenotypes, which are often masked by conventional measurements that average over cell populations. Although most studies on this topic have used microorganisms, differentiated mammalian cells have rarely been explored. Here, we report that only approximately 40% of clonal human embryonic kidney 293 cells respon...
متن کاملOrigin sites of calcium release and calcium oscillations in frog sympathetic neurons.
In many neurons, Ca(2+) signaling depends on efflux of Ca(2+) from intracellular stores into the cytoplasm via caffeine-sensitive ryanodine receptors (RyRs) of the endoplasmic reticulum. We have used high-speed confocal microscopy to image depolarization- and caffeine-evoked increases in cytoplasmic Ca(2+) levels in individual cultured frog sympathetic neurons. Although caffeine-evoked Ca(2+) w...
متن کاملA calcium-induced calcium release mechanism supports luteinizing hormone-induced testosterone secretion in mouse Leydig cells.
Leydig cells are responsible for the synthesis and secretion of testosterone, processes controlled by luteinizing hormone (LH). Binding of LH to a G protein-coupled receptor in the plasma membrane results in an increase in cAMP and in intracellular Ca(2+) concentration ([Ca(2+)](i)). Here we show, using immunofluorescence, that Leydig cells express ryanodine receptors (RyRs) and inositol 1,4,5-...
متن کامل