Correspondence to: Alan Fein, Dept. of Physiology, University of Connecticut Health Center, Farmington CT, 06030-3505. Fax:860-679-1269 E-mail:afein{at}neuron.uchc.edu.
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Changes in cytosolic free calcium ([Ca2+]i) often take the form of a sustained response or repetitive oscillations. The frequency and amplitude of [Ca2+]i oscillations are essential for the selective stimulation of gene expression and for enzyme activation. However, the mechanism that determines whether [Ca2+]i oscillates at a particular frequency or becomes a sustained response is poorly understood. We find that [Ca2+]i oscillations in rat megakaryocytes, as in other cells, results from a Ca2+-dependent inhibition of inositol 1,4,5-trisphosphate (IP3)induced Ca2+ release. Moreover, we find that this inhibition becomes progressively less effective with higher IP3 concentrations. We suggest that disinhibition, by increasing IP3 concentration, of Ca2+-dependent inhibition is a common mechanism for the regulation of [Ca2+]i oscillations in cells containing IP3-sensitive Ca2+ stores.
Key Words: megakaryocyte, protein kinase C, pleckstrin, IP3-5-phosphatase, platelets
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Calcium is a universal intracellular signaling agent involved in a myriad of processes from fertilization to cell death (
Many models of agonist-induced [Ca2+]i oscillations in nonexcitable cells require some form of Ca2+-dependent inhibition of IP3-induced Ca2+ release as a fundamental component (
![]() |
METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The methods used in these experiments have been fully described in previous publications (
Rat Megakaryocytes
Bone marrow is obtained from the tibial and femoral bones of adult Wistar rats. After filtration through a 75-µm nylon mesh to eliminate large masses of cells, the bone marrow suspension is spun and washed twice before incubation in standard external solution containing (mM): 140 NaCl, 5 KCl, 1 MgCl2, 2 CaCl2, 10 glucose, 10 HEPES, pH 7.4, supplemented by 0.1% BSA. Megakaryocytes are clearly distinguished from other bone marrow cells on the basis of their large size (2550 µm) and multilobular nucleus (
measurement of [Ca2+]i and Photolysis of Caged Compounds
Megakaryocytes are viewed through a coverslip forming the bottom of the recording chamber using a Diaphot microscope equipped with a Fluor 100x 1.3 NA oil immersion lens (Nikon Inc.). Single cell fluorometry is accomplished using an Ionoptix photon-counting fluorescence subsystem with a dual excitation light source (designed by Dr. D. Tillotson; Ionoptix) using Oregon Green 488 BAPTA-1 (OGB488) as the [Ca2+]i indicator. fluorescence intensity is measured on-line using the Ionwizard program (IonOptix). For photolysis of caged compounds, pulses of ultra violet light (290370 nm) are applied to the cell through the second channel of the dual excitation light source. Calibration of photolysis in the microscope was by measurement of the fluorescence change produced in the pH dye 2',7'-bis(carboxy-ethyl)-5(6)-carboxyfluorescein by protons released during the photolysis of NPE-caged ATP (
Chemicals
The "cell-permeant" AM ester and the "cell-impermeable" hexapotassium salt of OGB488 are obtained from molecular Probes, Inc. Caged IP3 and caged GPIP2 [1-(alpha-glycerophosphoryl)-myo-inositol 4,5-diphosphate, P4(5)-1-(2-nitrophenyl) ethyl ester] are from Calbiochem Corp. GF109203X is from Biomol and 2,3-diphosphoglycerate (2,3-DPG) is from Sigma Chemical Co.
Cell Loading of Caged Compounds
The cell-permeant AM ester of OGB488 is dissolved in DMSO and stored at -20°C. For the experiments not using patch clamping, cells are transferred onto glass coverslips and incubated with 2.55 µM OGB488/AM for 30 min. For the experiment with caged calcium, the cells are first incubated with 1030 µM caged calcium for at least 2 h. The final concentration of DMSO is always <0.1%. The coverslips with adherent cells are then washed several times with the standard external solution, and kept in the dark until use. For the other experiments, caged IP3 or caged GPIP2 together with OGB488 hexapotassium salt are included in the intrapipette solution at 100 and 200 µM, respectively [composition (mM): 20 KCl, 120 K-glutamate, 1 MgCl, 2 Na-GTP, 10 HEPES, pH 7.3]. Standard whole-cell patch-clamp recording techniques are used to voltage clamp and internally dialyze single megakaryocytes. Membrane current is monitored using an Axopatch-1D patch clamp amplifier (Axon Instruments). For most cells, 56 min is required for the OGB488 fluorescence signal to equilibrate in the patch-clamped cell.
Agonist Application
ADP or the mixture of ADP with GF109203X are dissolved in the standard external solution and applied directly to single megakaryocytes using a DAD-6 computer-controlled local superfusion system (ALA Scientific Instruments, Inc.). The output tube of the micromanifold (100 µm inside diameter) is placed within ~200 µm of the cell and the puff pressure is adjusted to achieve rapid agonist application while avoiding any mechanical disturbance of the cell.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
To study Ca2+-dependent inhibition of IP3-induced Ca2+ release, we performed paired-pulse experiments in rat megakaryocytes that are a convenient model for studying Ca2+ signaling in nonexcitable cells, because they express only an IP3-sensitive Ca2+ store and lack a ryanodine-sensitive Ca2+ store (
|
|
In rat basophilic leukemia cells, maximal desensitization of the response to the second pulse of IP3 is observed for a first pulse of IP3 that produced a [Ca2+]i response of near maximal amplitude (
We found that maximal desensitization was observed when the flash duration in a paired-pulse experiment produced a response just below that which gives a response of saturating amplitude. An example of such an experiment can be seen in Fig 2 A for which, after the release of Ca2+ produced by the photorelease of IP3, there is a period of desensitization during which a subsequent increase in IP3 releases less calcium. As the time interval between the pulses of IP3 increases, the response to the second pulse recovers back to that of the first. The desensitization is not due to emptying of the Ca2+ stores, because desensitization of the second response disappears if the duration of the second flash is increased threefold, thereby saturating the amplitude of the second response (n = 6 cells, data not shown). The desensitization also disappears if the duration of both flashes is increased three- to fourfold, thereby saturating the response amplitude of the response to each flash (n = 3 cells, data not shown). These findings are similar to what was found for rat basophilic leukemia cells (
The experiments described above establish the basic conditions for measuring the time course of recovery in a paired-pulse experiment. Having established these conditions, we can now turn to the central question of this investigation, whether Ca2+-dependent inhibition of IP3-induced Ca2+ release becomes progressively less effective with higher IP3 concentrations. For this purpose, we used procedures that would increase the lifetime of IP3, by slowing down its hydrolysis. We began by comparing the time course for the recovery from desensitization produced by IP3 injection with the time course for recovery from desensitization produced by injection of a hydrolysis-resistant analogue of IP3, namely GPIP2. GPIP2 is a less potent but fully active analogue of IP3 that is poorly metabolized, and the caged form of GPIP2 has been used to mobilize Ca2+ from IP3-sensitive Ca2+ stores (
Accordingly, in Fig 3, we compare the time course for recovery after photorelease of IP3, in the presence and absence of 2,3-DPG (2,3-diphosphoglycerate), an inhibitor of the IP3-5-phosphatase (
|
![]() |
(1) |
In Equation 1, the 1.5-s time delay is the approximate time to peak for the response to IP3 or GPIP2. For IP3 alone, = 15 s (n = 8 cells) and for IP3 with 2,3-DPG,
= 4.2 s (n = 6 cells). Also included in Fig 3 are recovery data for GPIP2 that were fit with
= 2.6 s (n = 5 cells) and data for IP3 in the presence of GF109203X, which were fit with
= 5.4 s (n = 11 cells).
GF109203X is a cell-permeable inhibitor of PKC that has been used effectively to inhibit PKC in platelets (
To be certain that the findings in Fig 3 are not somehow the result of an effect of GF109203X, 2,3-DPG, or GPIP2 on the power dependence of IP3-induced Ca2+ release, we carried out the experiment presented in Fig 4. The data in Fig 4 clearly show that the power dependence for GPIP2- and IP3-induced Ca2+ release in the presence of GF109203X or 2,3-DPG are no different than the power dependence of IP3-induced Ca2+ release itself. The flash duration that produced a response of half the maximal amplitude was 108 ± 39 ms (n = 8 cells) for GPIP2, 155 ± 54 ms (n = 5 cells) for IP3 in the presence of 2,3-DPG, and 121 ± 44 ms (n = 8 cells) for IP3 in the presence of GF109203X. The flash duration for half-maximal amplitude for GPIP2 and IP3 in the presence of GF109203X are significantly different than that for IP3 at the P = 0.05 level using the unpaired Student's t test. However, the flash duration for half-maximal amplitude for IP3 in the presence of 2,3-DPG is not significantly different than that for IP3. Hence the findings in Fig 3 are consistent with our suggestion that the extent of Ca2+-dependent inhibition is diminished when the lifetime of IP3 is increased.
|
Based on the data in Fig 2 and Fig 3, we predict that the falling phase of the response to the uncaging of GPIP2 should be dominated by the inhibitory effect of elevated [Ca2+]i on further Ca2+ release and the removal of Ca2+ from the cytoplasm. That is, the hydrolysis of GPIP2 by the 5-phosphatase should have minimal effect on the falling phase of the response. Accordingly, the falling phase of the response to the uncaging of GPIP2 should be greatly prolonged when compared with that for the uncaging of IP3, especially as the amount of IP3 or GPIP2 uncaged is increased. In Fig 5, we compare the time course of the [Ca2+]i response to the uncaging of IP3 with that for the uncaging of GPIP2. As the duration of the uncaging flash is increased from 150 to 2,000 ms, it can be seen that the falling phase of the response to GPIP2 is greatly prolonged when compared with that for IP3. Results similar to those in Fig 5 were seen in two additional cells each.
|
As mentioned above, Ca2+-dependent inhibition of IP3-mediated Ca2+ release is thought to play a central role in the generation of [Ca2+]i oscillations. Also, megakaryocytes exhibit [Ca2+]i oscillations when exposed to ADP (
|
The results in Fig 6 are very similar to those obtained by examining the effect of another PKC inhibitor, staurosporine, on ATP-induced [Ca2+]i oscillations monitored as a calcium-activated potassium current oscillation (
|
Based on the data of Fig 2, Fig 3, and Fig 6, we would expect that in response to multiple injections of IP3, the rise in [Ca2+]i would become plateau-like when the hydrolysis of IP3 is slowed down. Accordingly, in Fig 8, we compare the responses to multiple flashes, which photorelease IP3, in the presence and absence of 2,3-DPG. As can be seen in Fig 8 A, the response to the first flash that photoreleases IP3 is large, and the responses to subsequent flashes are greatly reduced in amplitude. Based on the results presented in Fig 2 and Fig 3, the finding in Fig 8 A is as expected. In contrast, in the experiment of Fig 8 B, in which 10 mM 2,3-DPG was included in the patch pipette to inhibit the IP3-5-phosphatase, a series of flashes that photorelease IP3 produce a sustained elevation of [Ca2+]i. Likewise a series of flashes that photorelease IP3 produce a sustained elevation of [Ca2+]i in the presence of GF109203X (Fig 8 D). Furthermore, a train of flashes that photorelease the hydrolysis-resistant IP3-analogue GPIP2 also produce a sustained elevation of [Ca2+]i (Fig 8 C).
|
The simplified diagram in Fig 9 summarizes our findings, emphasizing the dual regulation of calcium mobilization by IP3. For the sake of simplicity, GPIP2 has been left out of the figure. The heavy lines in Fig 9 are meant to represent the release of Ca2+ by IP3 and the disinhibition of Ca2+-dependent inhibition of IP3-mediated Ca2+ release by increasing IP3 concentration. We show this disinhibition as acting via calmodulin because recently published experiments have indicated that Ca2+-dependent inhibition of IP3 -mediated Ca2+ release for the type 1 IP3 receptor (IP3-R) is mediated by calmodulin (
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Our results demonstrate for the first time an important property of [Ca2+]i signaling in intact cells: an increase in the lifetime of IP3 brings about a decrease in Ca2+-dependent inhibition. These findings suggest a mechanism by which high concentrations of intracellular IP3 can cause cells to maintain an elevated level of [Ca2+]i. Indeed, this may explain the occurrence of sustained [Ca2+]i elevations at high agonist concentrations (
Since platelets express primarily the type 1 isoform of the IP3-R (
The observation that Ca2+-dependent inhibition of the type 1 IP3-R is mediated by calmodulin implies that inhibition of calmodulin should disinhibit Ca2+-dependent inhibition of IP3-mediated Ca2+ release (
Whether or not these properties of the type I receptor also belong to the type II and III IP3-Rs is problematic. Recent single-channel bilayer recordings from the type II and III receptors indicate that they do not exhibit Ca2+-dependent inhibition (
One of the striking features of IP3-mediated Ca2+ release in megakaryocytes is the highly nonlinear dependence between IP3 and peak Ca2+ (Fig 1 and Fig 4). In other cell types, the dependence is not as steep (
It might be argued that as the result of inhibition of the 5-phosphatase by 2,3-DPG, more IP3 is converted by the IP3-3-kinase to inositol 1,3,4,5-tetrakisphosphate (IP4). IP4 has been shown to enhance the amount of Ca2+ mobilized by submaximal concentrations of IP3 in the L1210 cell line (
Although the findings reported here were obtained in megakaryocytes, they should be relevant to calcium mobilization in platelets also; in as much as megakaryocytes are the precursors of platelets. Specifically, we speculate that our findings suggest a role for pleckstrin, which is a major substrate for PKC in platelets, in regulating [Ca2+]i oscillations by regulating the lifetime of IP3.
![]() |
Footnotes |
---|
Dr. Tertyshnikova's present address is Bristol-Myers Squibb Co., Pharmaceutical Research Institute, Wallingford, CT 06492-7660.
1 Abbreviations used in this paper: IP3, inositol 1,4,5-trisphosphate; IP3-R, IP3 receptor.
![]() |
Acknowledgements |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
We thank Drs. L. Jaffe, R. Shaafi, M. Terasaki, and J. Watras for their constructive criticisms of an earlier version of this manuscript.
Submitted: 29 September 1999
Revised: 22 February 2000
Accepted: 28 February 2000
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Benevolensky, D., Moraru, I.I., Watras, J. 1994. Micromolar calcium decreases affinity of inositol trisphosphate receptor in vascular smooth muscle. Biochem. J. 299:631-636[Medline].
Berridge, M.J., Bootman, M.D., Lipp, P. 1998. Calciuma life and death signal. Nature 395:645-648[Medline].
Berven, L.A., Barritt, G.J. 1994. A role for a pertussis toxinsensitive trimeric G-protein in store-operated Ca2+ inflow in hepatocytes. FEBS Lett. 346:235-240[Medline].
Bezprozvanny, I., Watras, J., Ehrlich, B.E. 1991. Bell-shaped calcium-response curves of Ins(1,4,5)P3- and calcium-gated channels from endoplasmic reticulum of cerebellum. Nature 351:751-754[Medline].
Bootman, M.D., Missiaen, L., Parys, J.B., De Smedt, H., Casteels, R. 1995. Control of inositol 1,4,5-trisphosphateinduced Ca2+ release by cytosolic Ca2+. Biochem. J. 306:445-451[Medline].
Carter, T.D., Ogden, D. 1997. Kinetics of Ca2+ release by InsP3 in pig single aortic endothelial cells: evidence for an inhibitory role of cytosolic Ca2+ in regulating hormonally evoked Ca2+ spikes. J. Physiol. 504:17-33[Abstract].
Combettes, L., Hannaert-Merah, Z., Coquil, J.F., Rousseau, C., Claret, M., Swillens, S., Champeil, P. 1994. Rapid filtration studies of the effect of cytosolic Ca2+ on inositol 1,4,5-trisphosphateinduced 45Ca2+ release from cerebellar microsomes. J. Biol. Chem. 269:17561-17571
De Koninck, P., Schulman, H. 1998. Sensitivity of CaM kinase II to the frequency of Ca2+ oscillations. Science. 279:227-230
Dolmetsch, R.E., Xu, K., Lewis, R.S. 1998. Calcium oscillations increase the efficiency and specificity of gene expression. Nature. 392:933-936[Medline].
Fewtrell, C. 1993. Ca2+ oscillations in non-excitable cells. Annu. Rev. Physiol. 55:427-454[Medline].
Fink, C.C., Slepchenko, B., Loew, L.M. 1999. Determination of time-dependent inositol-1,4,5-trisphosphate concentrations during calcium release in a smooth muscle cell. Biophys. J. 77:617-628
Hagar, R.E., Burgstahler, A.D., Nathanson, M.H., Ehrlich, B.E. 1998. Type III InsP3 receptor channel stays open in the presence of increased calcium. Nature. 396:81-84[Medline].
Hannaert-Merah, Z., Combettes, L., Coquil, J.F., Swillens, S., Mauger, J.P., Claret, M., Champeil, P. 1995. Characterization of the co-agonist effects of strontium and calcium on myo-inositol trisphosphate-dependent ion fluxes in cerebellar microsomes. Cell Calc. 18:390-399[Medline].
Heemskerk, J.W., Vis, P., Feijge, M.A., Hoyland, J., Mason, W.T., Sage, S.O. 1993. Roles of phospholipase C and Ca(2+)-ATPase in calcium responses of single, fibrinogen-bound platelets. J. Biol. Chem. 268:356-363
Iino, M. 1990. Biphasic Ca2+ dependence of inositol 1,4,5-trisphosphate-induced Ca release in smooth muscle cells of the guinea pig taenia caeci. J. Gen. Physiol 95:1103-1122[Abstract].
Ilyin, V., Parker, I. 1994. Role of cytosolic Ca2+ in inhibition of InsP3-evoked Ca2+ release in Xenopus oocytes. J. Physiol. 477:503-509[Abstract].
Irvine, R.F. 1992. Is inositol tetrakisphosphate the second messenger that controls Ca2+ entry into cells? Adv. Second Messenger Phosphoprotein Res. 26:161-185[Medline].
Jacob, R., Merritt, J.E., Hallam, T.J., Rink, T.J. 1988. Repetitive spikes in cytoplasmic calcium evoked by histamine in human endothelial cells. Nature. 335:40-45[Medline].
Joseph, S.K., Rice, H.L., Williamson, J.R. 1989. The effect of external calcium and pH on inositol trisphosphate-mediated calcium release from cerebellum microsomal fractions. Biochem. J 258:261-265[Medline].
Kaftan, E.J., Ehrlich, B.E., Watras, J. 1997. Inositol 1,4,5-trisphosphate (InsP3) and calcium interact to increase the dynamic range of InsP3 receptor-dependent calcium signaling. J. Gen. Physiol. 110:529-538
Kapural, L., Fein, A. 1997. Changes in the expression of voltage-gated K+ currents during development of human megakaryocytic cells. Biochim. Biophys. Acta. 1326:319-328[Medline].
Khodakhah, K., Ogden, D. 1995. Fast activation and inactivation of inositol trisphosphate-evoked Ca2+ release in rat cerebellar Purkinje neurones. J. Physiol 487:343-358[Abstract].
King, W.G., Rittenhouse, S.E. 1989. Inhibition of protein kinase C by staurosporine promotes elevated accumulations of inositol trisphosphates and tetrakisphosphate in human platelets exposed to thrombin. J. Biol. Chem 264:6070-6074
Li, W., Llopis, J., Whitney, M., Zlokarnik, G., Tsien, R.Y. 1998. Cell-permeant caged InsP3 ester shows that Ca2+ spike frequency can optimize gene expression. Nature. 392:936-941[Medline].
Loomis-Husselbee, J.W., Cullen, P.J., Dreikausen, U.E., Irvine, R.F., Dawson, A.P. 1996. Synergistic effects of inositol 1,3,4,5-tetrakisphosphate on inositol 2,4,5-triphosphate-stimulated Ca2+ release do not involve direct interaction of inositol 1,3,4,5-tetrakisphosphate with inositol triphosphate-binding sites. Biochem. J. 314:811-816[Medline].
Loomis-Husselbee, J.W., Walker, C.D., Bottomley, J.R., Cullen, P.J., Irvine, R.F., Dawson, A.P. 1998. Modulation of Ins(2,4,5)P3-stimulated Ca2+ mobilization by Ins(1,3,4, 5)P4: enhancement by activated G-proteins, and evidence for the involvement of a GAP1 protein, a putative Ins(1,3,4,5)P4 receptor. Biochem. J. 331:947-952[Medline].
Lu, X., Fein, A., Feinstein, M.B., O'Rourke, F.A. 1999. Antisense knock out of the inositol 1,3,4,5-tetrakisphosphate receptor GAP1(IP4BP) in the human erythroleukemia cell line leads to the appearance of intermediate conductance K(Ca) channels that hyperpolarize the membrane and enhance calcium influx. J. Gen. Physiol. 113:81-96
Mak, D.O.D., McBride, S., Foskett, J.K. 1998. Inositol 1,4,5-tris-phosphate activation of inositol tris-phosphate receptor Ca2+ channel by ligand tuning of Ca2+ inhibition. Proc. Natl. Acad. Sci. USA 95:15821-15825
Michikawa, T., Hirota, J., Kawano, S., Hiraoka, M., Yamada, M., Furuichi, T., Mikoshiba, K. 1999. Calmodulin mediates calcium-dependent inactivation of the cerebellar type 1 inositol 1,4,5-trisphosphate receptor. Neuron. 23:799-808[Medline].
Oancea, E., Meyer, T. 1996. Reversible desensitization of inositol trisphosphate-induced calcium release provides a mechanism for repetitive calcium spikes. J. Biol. Chem. 271:17253-17260
Ogden, D., Capiod, T. 1997. Regulation of Ca2+ release by InsP3 in single guinea pig hepatocytes and rat Purkinje neurons. J. Gen. Physiol. 109:741-756
Ogden, D.C., Capiod, T., Walker, J.W., Trentham, D.R. 1990. Kinetics of the conductance evoked by noradrenaline, inositol trisphosphate or Ca2+ in guinea-pig isolated hepatocytes. J. Physiol. 422:585-602[Abstract].
O'Rourke, F., Matthews, E., Feinstein, M.B. 1995. Purification and characterization of the human type 1 Ins(1,4,5)P3 receptor from platelets and comparison with receptor subtypes in other normal and transformed blood cells. Biochem. J. 312:499-503[Medline].
Papp, B., Paszty, K., Kovacs, T., Sarkadi, B., Gardos, G., Enouf, J., Enyedi, A. 1993. Characterization of the inositol trisphosphatesensitive and insensitive calcium stores by selective inhibition of the endoplasmic reticulum-type calcium pump isoforms in isolated platelet membrane vesicles. Cell Calc. 14:531-538[Medline].
Payne, R., Flores, T.M., Fein, A. 1990. Feedback inhibition by calcium limits the release of calcium by inositol trisphosphate in Limulus ventral photoreceptors. Neuron. 4:547-555[Medline].
Payne, R., Walz, B., Levy, S., Fein, A. 1988. The localization of calcium release by inositol trisphosphate in Limulus photoreceptors and its control by negative feedback. Philos. Trans. R. Soc. Lond. B Biol. Sci. 320:359-379[Medline].
Petersen, C.C., Toescu, E.C., Potter, B.V., Petersen, O.H. 1991. Inositol triphosphate produces different patterns of cytoplasmic Ca2+ spiking depending on its concentration. FEBS Lett. 293:179-182[Medline].
Putney, J.W., Jr., Bird, G.S. 1993. The inositol phosphate-calcium signaling system in nonexcitable cells. Endocr. Rev 14:610-631[Medline].
Quinton, T.M., Dean, W.L. 1996. Multiple inositol 1,4,5-trisphosphate receptor isoforms are present in platelets. Biochem. Biophys. Res. Commun. 224:740-746[Medline].
Ramos-Franco, J., Fill, M., Mignery, G.A. 1998. Isoform-specific function of single inositol 1,4,5-trisphosphate receptor channels. Biophys. J. 75:834-839
Shears, S.B. 1989. Metabolism of the inositol phosphates produced upon receptor activation. Biochem. J. 260:313-324[Medline].
Supattapone, S., Worley, P.F., Baraban, J.M., Snyder, S.H. 1988. Solubilization, purification, and characterization of an inositol trisphosphate receptor. J. Biol. Chem. 263:1530-1534
Taylor, C.W. 1998. Inositol trisphosphate receptors: Ca2+-modulated intracellular Ca2+ channels. Biochim. Biophys. Acta. 1436:19-33[Medline].
Tertyshnikova, S., Fein, A. 1997. [Ca2+]i oscillations and [Ca2+]i waves in rat megakaryocytes. Cell Calc 21:331-344[Medline].
Tertyshnikova, S., Fein, A. 1998. Inhibition of inositol 1,4,5-trisphosphate-induced Ca2+ release by cAMP-dependent protein kinase in a living cell. Proc. Natl. Acad. Sci. USA. 95:1613-1617
Tertyshnikova, S., Yan, X., Fein, A. 1998. cGMP inhibits IP3-induced Ca2+ release in intact rat megakaryocytes via cGMP- and cAMP-dependent protein kinases. J. Physiol. 512:89-96
Toullec, D., Pianetti, P., Coste, H., Bellevergue, P., Grand-Perret, T., Ajakane, M., Baudet, V., Boissin, P., Boursier, E., Loriolle, F. et al. 1991. The bisindolylmaleimide GF 109203X is a potent and selective inhibitor of protein kinase C. J. Biol. Chem. 266:15771-15781
Uneyama, H., Uneyama, C., Akaike, N. 1993. Intracellular mechanisms of cytoplasmic Ca2+ oscillation in rat megakaryocyte. J. Biol. Chem. 268:168-174
Wakui, M., Potter, B.V., Petersen, O.H. 1989. Pulsatile intracellular calcium release does not depend on fluctuations in inositol trisphosphate concentration. Nature. 339:317-320[Medline].
Wood, S.F., Szuts, E.Z., Fein, A. 1990. Metabolism of inositol 1,4,5-trisphosphate in squid photoreceptors. J. Comp. Physiol. 160:293-298. [B].