Biomedical subjects

Tasmina A Goraya

Publications and source records attributed to Tasmina A Goraya.

3 recordsLinked to original sources

PubMed2005

Ca2+-calmodulin-dependent phosphodiesterase (PDE1): current perspectives.

Ca2+-calmodulin-dependent phosphodiesterases (PDE1), like Ca2+-sensitive adenylyl cyclases (AC), are key enzymes that play a pivotal role in mediating the cross-talk between cAMP and Ca2+ signalling. Our understanding of how ACs respond to Ca2+ has advanced greatly, with significant breakthroughs at both the molecular and functional level. By contrast, little is known of the mechanisms that might underlie the regulation of PDE1 by Ca2+ in the intact cell. In living cells, Ca2+ signals are complex and diverse, exhibiting different spatial and temporal properties. The potential therefore exists for dynamic changes in the subcellular distribution and activation of PDE1 in relation to intracellular Ca2+ dynamics. PDE1s are a large family of multiply-spliced gene products. Therefore, it is possible that a cell-type specific response to elevation in [Ca2+]i can occur, depending on the isoform of PDE1 expressed. In this article, we summarize current knowledge on Ca2+ regulation of PDE1 in the intact cell and discuss approaches that might be undertaken to delineate the responses of this important group of enzymes to changes in [Ca2+]i.

Animals↗

PubMed2004

Sustained entry of Ca2+ is required to activate Ca2+-calmodulin-dependent phosphodiesterase 1A.

Regulation of adenylyl cyclases (ACs) by Ca2+ requires capacitative Ca2+ entry (CCE) (Cooper, D. M. F. (2003) Biochem. J. 375, 517-529), but whether Ca2+-sensitive phosphodiesterases (PDEs) are similarly discriminating has never been addressed. In the present study, a variety of conditions were devised to manipulate [Ca2+]i so that we could ask whether PDE1 selectively responds to different modes of elevating [Ca2+]i, viz. Ca2+ released from intracellular stores and various modes of Ca2+ entry. In 1321N1 human astrocytoma cells, the endogenous PDE1 (identified as PDE1A by reverse transcriptase-PCR) was largely insensitive to Ca2+ released from carbachol-sensitive stores but was robustly stimulated by a similar rise in [Ca2+]i due to carbachol-induced Ca2+ influx. Gd3+, which effectively blocked thapsigargin-induced CCE and its effect on PDE1A, also inhibited the activation of PDE1A by carbachol-induced Ca2+ entry. However, non-selective ionomycin-mediated Ca2+ entry also activated PDE1A, so that, unlike Ca2+-sensitive ACs, PDE1A cannot discriminate between the different sources of Ca2+ entry. Fractionation of the cells revealed that the Ca2+-calmodulin-stimulated PDE activity was not present at the plasma membrane but was associated with the cytosol and the organellar compartments of the cell. Therefore, the apparent disparity between PDE1A and ACs is likely to be the consequence of their differential subcellular localization. Nevertheless, in a physiological context, where artificial modes of elevating [Ca2+]i are not available, as with ACs, a dependence on CCE would be evident, and it would be the duration of this influx of Ca2+ that would determine how long PDE1A was activated.

Adenylyl Cyclases↗

PubMed2003

Parathyroid hormone increases the sensitivity of inositol trisphosphate receptors by a mechanism that is independent of cyclic AMP.

1 In fura 2-loaded HEK-293 cells stably expressing human type 1 parathyroid hormone (PTH) receptors, PTH potentiated the Ca(2+) mobilization evoked by carbachol by >4 fold without itself increasing the intracellular [Ca(2+)]. 2 PTH potentiated the Ca(2+) release evoked by a cell-permeant analogue of inositol 1,4,5-trisphosphate (InsP(3)BM). 3 Prolonged incubation with InsP(3)BM emptied the Ca(2+) stores as effectively as PTH in combination with a maximal concentration of carbachol, indicating that PTH did not increase the size of the InsP(3)-sensitive Ca(2+) pool. 4 Responses to PTH were unaffected by disruption of the cytoskeleton. 5 The EC(50) for carbachol-evoked Ca(2+) release and InsP(3) formation were indistinguishable (approximately 40 microM), consistent with even the highest concentrations of carbachol generating insufficient InsP(3) to release the entire InsP(3)-sensitive Ca(2+) pool. 6 Inhibition of cyclic AMP-dependent protein kinase A (PKA), using H89 or CMIQ, did not affect potentiation of carbachol-evoked Ca(2+) signals by PTH. 7 SQ22536 or DDA, inhibitors of adenylyl cyclase, inhibited PTH-evoked cyclic AMP formation and IBMX, an inhibitor of cyclic nucleotide phosphodiesterase, increased the amount of cyclic AMP detected after stimulation by PTH. None of these drugs affected the potentiation of Ca(2+) signals by maximal or submaximal concentrations of PTH. 8 We conclude that PTH potentiates the Ca(2+) release evoked by receptors that stimulate InsP(3) formation by sensitizing InsP(3) receptors through a cyclic AMP-independent mechanism.

Calcium↗