Calcium store depletion potentiates a phosphodiesterase inhibitor‐ and dibutyryl cGMP‐evoked calcium influx in rat pituitary GH₃ cells

Abstract

A role for cGMP in the control of capacitative Ca 2+ two [9]. Also, it has been suggested that the calcium-releaseinflux was identified in rat pituitary GH3 cells. Application of activated calcium (CRAC) channel, involved in capacitative 50 ~tM-1 mM of the non-specific phosphodiesterase inhibitor, Ca 2+ influx, might be analogous to the transient receptor 3-isobutyl-l-methylxanthine (IBMX), or the specific cGMPpotential (trp) gene product in Drosophila photoreceptors phosphodiesterase inhibitor, zaprinast, induced a dose-dependent [6], which has been shown to possess significant amino acid Preparation of cellsRat pituitary GH3 cells were seeded onto polylysine-coated borosi-1. Introduction licate glass cover-slips in 6-well plates, and were grown in Hams F10 medium supplemented with 16% foetal calf serum for 34 days. For Ca 2+ imaging experiments, cells were loaded with 2 ~tM fura-2 AM in The cyclic nucleotides, cGMP and cAMP, have long been 2 ml Hank's medium (pH 7.2) in the presence of 0.1% Pluronic for 45 established as important second messengers in a variety of cell min at room temperature. Cover slips were rinsed in Hank's medium signalling pathways [1,2]. Roles for these species in intraceland were then transferred to a teflon cover-slip holder and 900 p3 lular Ca 2+ signalling and homeostasis are also apparent. Most Hank's medium added. The cover-slip dish was placed on the stage of an inverted Zeiss Axiovert 35 microscope for Ca 2+ imaging. notably, cAMP stimulates Ca r+ influx through L-type Ca r+ channels of rat pancreatic [~-cells [3] Video ratio image analysis of GH3 cell [Ca2+]i was performed using an ion imaging system supplied by 'Improvision', Coventry, UK, in a channels [1], inhibits Ca r+ influx in other excitable cells by similar way as previously described [5]. Cells were loaded with the directly affecting voltage-gated Ca r+ channels [4], and moduacetoxymethyl (AM) ester of Fura-2 (Molecular Probes Inc.). Free lates Ca r+ influx in non-excitable cells [4]. In addition, cGMP cytosolic Ca 2+ concentration was determined by taking the ratio of has also been shown to stimulate the synthesis of the potent fluorescence intensities at excitation wavelengths 340 and 380 nm, Ca r+ mobilizing agent, cylic-ADP-ribose, in sea urchin eggs using an emission wavelength of 510 nm. Pairs of 340 and 380 nm images were captured every 3 s and ratio images were calculated using [5]. Although the above indicate specific roles for cyclic nu-

Characterization of action potential waveform-evoked L-type calcium currents in pituitary GH 3 cells

“…The extent to which Ca 2+ entry through AP-evoked I Ca,L contributes to store-operated Ca 2+ entry in excitable cells remains to be determined. Indeed, Ca 2+ influx in GH 3 cells induced by the depletion of Ca 2+ stores can be abolished by further addition of nicardipine, a blocker of I Ca,L (Willmott et al 1996). Additionally, the present results could be compatible with a recent study showing the exclusion of the diffusible messengers for store-operated Ca 2+ current (Yao et al 1999).…”

A Fundamental Role for the Nitric Oxide-G-Kinase Signaling Pathway in Mediating Intercellular Ca2+Waves in Glia

“…Recent interest has focussed on specific roles for NO-Gkinase signaling in regulating store-operated Ca 2ϩ influx and Ca 2ϩ influx pathways that are dependent on the state of filling of intracellular Ca 2ϩ stores (Xu et al, 1994;Bischof et al, 1995;Mathes and Thompson, 1996;Willmott et al, 1996a) and also Ca 2ϩ mobilization via the increased synthesis of the Ca 2ϩ mobilizing agent cyclic ADP-ribose (Clementi et al, 1996;Willmott et al, 1996c). Cyclic ADP-ribose (cADPR) appears to release Ca 2ϩ from ER Ca 2ϩ stores via RyRs and is considered to be a putative modulator of calcium-induced calcium release (Galione et al, 1991).…”

Functional importance of the dihydropyridine‐sensitive, yet voltage‐insensitive store‐operated Ca2+ influx of U937 cells

“…Fax: +44 171 9826076. factor (CIF) from Ca 2+ stores, or the direct coupling of Ca 2+ stores and plasma membrane channels [4]. Small G proteins may be implicated in SOC channel modulation [4], while CIF and cGMP might be analogous, since this cyclic nucleotide appears to potentiate Ca 2+ influx activated in response to Ca 2+ store depletion in a variety of cells [6][7][8][9]. It is noteworthy that the first SOC to be identified, the Ca 2+ releaseactivated Ca 2+ (CRAC) channel, has been proposed to be a mammalian homologue of the transient receptor potential (trp) gene product of Drosophila photoreceptors [4], which shares significant amino acid sequence homology to voltagegated Ca 2+ channels (VGCs) [10].…”