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ATP regulation of recombinant type 3 inositol 1,4,5-trisphosphate receptor gating.

Mak DO, McBride S, Foskett JK - J. Gen. Physiol. (2001)

Bottom Line: As [ATP]i was increased from 0 to 0.5 mM, maximum r-InsP3R-3 channel open probability (Po) remained unchanged, whereas the half-maximal activating [Ca2+]i and activation Hill coefficient both decreased continuously, from 800 to 77 nM and from 1.6 to 1, respectively, and the half-maximal inhibitory [Ca2+]i was reduced from 115 to 39 microM.These effects were largely due to effects of ATP on the mean closed channel duration.Possible molecular models to account for the distinct regulation by ATP of the Ca2+ activation properties of the two channel isoforms and the physiological implications of these results are discussed.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.

ABSTRACT
A family of inositol 1,4,5-trisphosphate (InsP3) receptor (InsP3R) Ca2+ release channels plays a central role in Ca2+ signaling in most cells, but functional correlates of isoform diversity are unclear. Patch-clamp electrophysiology of endogenous type 1 (X-InsP3R-1) and recombinant rat type 3 InsP3R (r-InsP3R-3) channels in the outer membrane of isolated Xenopus oocyte nuclei indicated that enhanced affinity and reduced cooperativity of Ca2+ activation sites of the InsP3-liganded type 3 channel distinguished the two isoforms. Because Ca2+ activation of type 1 channel was the target of regulation by cytoplasmic ATP free acid concentration ([ATP](i)), here we studied the effects of [ATP]i on the dependence of r-InsP(3)R-3 gating on cytoplasmic free Ca2+ concentration ([Ca2+]i. As [ATP]i was increased from 0 to 0.5 mM, maximum r-InsP3R-3 channel open probability (Po) remained unchanged, whereas the half-maximal activating [Ca2+]i and activation Hill coefficient both decreased continuously, from 800 to 77 nM and from 1.6 to 1, respectively, and the half-maximal inhibitory [Ca2+]i was reduced from 115 to 39 microM. These effects were largely due to effects of ATP on the mean closed channel duration. Whereas the r-InsP3R-3 had a substantially higher Po than X-InsP3R-1 in activating [Ca2+]i (< 1 microM) and 0.5 mM ATP, the Ca2+ dependencies of channel gating of the two isoforms became remarkably similar in the absence of ATP. Our results suggest that ATP binding is responsible for conferring distinct gating properties on the two InsP3R channel isoforms. Possible molecular models to account for the distinct regulation by ATP of the Ca2+ activation properties of the two channel isoforms and the physiological implications of these results are discussed. Complex regulation by ATP of the types 1 and 3 InsP3R channel activities may enable cells to generate sophisticated patterns of Ca2+ signals with cytoplasmic ATP as one of the second messengers.

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Ca2+ dependencies of types 1 and 3 InsP3R channel Po in the absence of ATP. Open triangles represent data for X-InsP3R-1 obtained from uninjected oocytes. Closed squares represent data for r-InsP3R-3 obtained from cRNA-injected oocytes. The curves (dashed for X-InsP3R-1 and solid for r-InsP3R-3) are the biphasic Hill equation fits using  and parameters tabulated in Table .
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Figure 5: Ca2+ dependencies of types 1 and 3 InsP3R channel Po in the absence of ATP. Open triangles represent data for X-InsP3R-1 obtained from uninjected oocytes. Closed squares represent data for r-InsP3R-3 obtained from cRNA-injected oocytes. The curves (dashed for X-InsP3R-1 and solid for r-InsP3R-3) are the biphasic Hill equation fits using and parameters tabulated in Table .

Mentions: In sharp contrast, the biphasic Ca2+ dependence of the r-InsP3R-3 in the absence of cytoplasmic free ATP is remarkably similar to the biphasic Ca2+ dependence of the X-InsP3R-1 in the absence of ATP (Fig. 5), with Pmax = 0.80 ± 0.02, Kact = 550 ± 50 nM, Hact = 1.9 ± 0.6, Kinh = 110 ± 15 μM, and Hinh = 4.0 ± 0.7 (Table ). Thus, in the absence of cytoplasmic ATP, there are no significant differences between the responses to Ca2+ of the types 1 and 3 InsP3R channels.


ATP regulation of recombinant type 3 inositol 1,4,5-trisphosphate receptor gating.

Mak DO, McBride S, Foskett JK - J. Gen. Physiol. (2001)

Ca2+ dependencies of types 1 and 3 InsP3R channel Po in the absence of ATP. Open triangles represent data for X-InsP3R-1 obtained from uninjected oocytes. Closed squares represent data for r-InsP3R-3 obtained from cRNA-injected oocytes. The curves (dashed for X-InsP3R-1 and solid for r-InsP3R-3) are the biphasic Hill equation fits using  and parameters tabulated in Table .
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2233659&req=5

Figure 5: Ca2+ dependencies of types 1 and 3 InsP3R channel Po in the absence of ATP. Open triangles represent data for X-InsP3R-1 obtained from uninjected oocytes. Closed squares represent data for r-InsP3R-3 obtained from cRNA-injected oocytes. The curves (dashed for X-InsP3R-1 and solid for r-InsP3R-3) are the biphasic Hill equation fits using and parameters tabulated in Table .
Mentions: In sharp contrast, the biphasic Ca2+ dependence of the r-InsP3R-3 in the absence of cytoplasmic free ATP is remarkably similar to the biphasic Ca2+ dependence of the X-InsP3R-1 in the absence of ATP (Fig. 5), with Pmax = 0.80 ± 0.02, Kact = 550 ± 50 nM, Hact = 1.9 ± 0.6, Kinh = 110 ± 15 μM, and Hinh = 4.0 ± 0.7 (Table ). Thus, in the absence of cytoplasmic ATP, there are no significant differences between the responses to Ca2+ of the types 1 and 3 InsP3R channels.

Bottom Line: As [ATP]i was increased from 0 to 0.5 mM, maximum r-InsP3R-3 channel open probability (Po) remained unchanged, whereas the half-maximal activating [Ca2+]i and activation Hill coefficient both decreased continuously, from 800 to 77 nM and from 1.6 to 1, respectively, and the half-maximal inhibitory [Ca2+]i was reduced from 115 to 39 microM.These effects were largely due to effects of ATP on the mean closed channel duration.Possible molecular models to account for the distinct regulation by ATP of the Ca2+ activation properties of the two channel isoforms and the physiological implications of these results are discussed.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.

ABSTRACT
A family of inositol 1,4,5-trisphosphate (InsP3) receptor (InsP3R) Ca2+ release channels plays a central role in Ca2+ signaling in most cells, but functional correlates of isoform diversity are unclear. Patch-clamp electrophysiology of endogenous type 1 (X-InsP3R-1) and recombinant rat type 3 InsP3R (r-InsP3R-3) channels in the outer membrane of isolated Xenopus oocyte nuclei indicated that enhanced affinity and reduced cooperativity of Ca2+ activation sites of the InsP3-liganded type 3 channel distinguished the two isoforms. Because Ca2+ activation of type 1 channel was the target of regulation by cytoplasmic ATP free acid concentration ([ATP](i)), here we studied the effects of [ATP]i on the dependence of r-InsP(3)R-3 gating on cytoplasmic free Ca2+ concentration ([Ca2+]i. As [ATP]i was increased from 0 to 0.5 mM, maximum r-InsP3R-3 channel open probability (Po) remained unchanged, whereas the half-maximal activating [Ca2+]i and activation Hill coefficient both decreased continuously, from 800 to 77 nM and from 1.6 to 1, respectively, and the half-maximal inhibitory [Ca2+]i was reduced from 115 to 39 microM. These effects were largely due to effects of ATP on the mean closed channel duration. Whereas the r-InsP3R-3 had a substantially higher Po than X-InsP3R-1 in activating [Ca2+]i (< 1 microM) and 0.5 mM ATP, the Ca2+ dependencies of channel gating of the two isoforms became remarkably similar in the absence of ATP. Our results suggest that ATP binding is responsible for conferring distinct gating properties on the two InsP3R channel isoforms. Possible molecular models to account for the distinct regulation by ATP of the Ca2+ activation properties of the two channel isoforms and the physiological implications of these results are discussed. Complex regulation by ATP of the types 1 and 3 InsP3R channel activities may enable cells to generate sophisticated patterns of Ca2+ signals with cytoplasmic ATP as one of the second messengers.

Show MeSH
Related in: MedlinePlus