Mak DO et al. (2001), ATP regulation of recombinant type 3 inositol 1...

XB-ART-9101

J Gen Physiol 2001 May 01;1175:447-56.

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

Mak DO , McBride S , Foskett JK .

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Species referenced: Xenopus
Genes referenced: hunk mak tbx2

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	Figure 1. Ca2+ dependencies of types 1 and 3 InsP3R channel Po in the presence of 0.5 mM ATP. 10 μM InsP3 was present in the pipet solutions used in experiments presented in all figures. 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 from Mak et al. 2001.
	Figure 2. (A–D) Typical single-channel current traces of r-InsP3R-3 channels in the outer membrane of nuclei isolated from r-InsP3R-3 cRNA-injected oocytes under suboptimal [Ca2+]i, with various [ATP]i and [Mg2+]i. Arrows indicate closed channel current levels. (A) [Ca2+]i = 224 nM, [ATP]i = 0.5 mM; [Mg2+]i = 0 mM. (B) [Ca2+]i = 255 nM, [ATP]i = 0 mM; [Mg2+]i = 0 mM. (C) [Ca2+]i = 274 nM, [ATP]i = 0 mM; [Mg2+]i = 3.0 mM. (D) [Ca2+]i = 286 nM, [ATP]i = 12 μM; [Mg2+]i = 2.5 mM (0.5 mM total ATP; 3 mM total Mg2+). Reduction of InsP3R channel conductance in the presence of Mg2+ (C and D) is caused by permeant ion block of the channel by the divalent cation (Mak and Foskett 1998). (E) Single-channel Po of the r-InsP3R-3 channel in conditions specified in A–D. Asterisk represents P < 0.05.
	Figure 3. (A–D) Typical single-channel current traces of r-InsP3R-3 channels under optimal [Ca2+]i with various [ATP]i and [Mg2+]i. Arrows indicate closed channel current levels. (A) [Ca2+]i = 4.4 μM, [ATP]i = 0.5 mM; [Mg2+]i = 0 mM. (B) [Ca2+]i = 5.6 μM, [ATP]i = 0 mM; [Mg2+]i = 0 mM. (C) [Ca2+]i = 2.5 μM, [ATP]i = 0 mM; [Mg2+]i = 3.0 mM. (D) [Ca2+]i = 2.5 μM, [ATP]i = 12 μM; [Mg2+]i = 2.5 mM (0.5 mM total ATP; 3 mM total Mg2+). Reduction of InsP3R channel conductance in the presence of Mg2+ (C and D) is caused by permeant ion block of the channel by the divalent cation (Mak and Foskett 1998). (E) Single-channel open probability (Po) of the r-InsP3R-3 channel in conditions specified in A–D.
	Figure 4. (A) Ca2+ dependencies of the r-InsP3R-3 channel Po in the presence of various [ATP]i. The symbols correspond to Po data in various [ATP]i (in millimolars) as tabulated in the graph. The curves for 0 and 0.5 mM ATP represent theoretical fits to the data using the biphasic Hill equation () whereas the curve for 0.3 mM ATP represents a fit using the activation Hill equation (). Hill equation parameters used are tabulated in Table . (B–C) Typical single-channel current traces of r-InsP3R-3 channels under inhibiting [Ca2+]i. Arrows indicate closed channel current levels. (B) [Ca2+]i = 58 μM, [ATP]i = 0.5 mM; [Mg2+]i = 0 mM. (C) [Ca2+]i = 83 μM, [ATP]i = 0 mM; [Mg2+]i = 0 mM.
	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 .
	Figure 6. Ca2+ dependencies of the mean open and closed channel durations of the r-InsP3R-3 channels in the presence of 0 (▪) or 0.5 mM (○) cytoplasmic free ATP. In the closed channel duration graph, data points obtained with the same InsP3 concentrations are connected with a line for clarity.
	Figure 7. Variation of the ratio between the Po of r-InsP3R-3 (3Po) and that of X–InsP3R-1 (1Po), with [Ca2+]i in the presence of different [ATP]i as tabulated. Po are calculated with , using the parameters (Pmax, Kact, and Hact) tabulated in Table . 3Po for 4.8 and 9.5 mM ATP were calculated using the same parameters as in 0.5 mM ATP. Pmax of X-InsP3R-1 was assumed to be 0.8 in 0.3 mM ATP.

References [+] :

Berridge, Inositol trisphosphate and calcium signalling. 1993, Pubmed