Free oxygen radicals(OFR) directly modify function of cardiac sarcoplasmic reticulum(SR) calcium-release channel.

Sphingosylphosphocholine (SPC) modulates Ca2+ release from isolated cardiac sarcoplasmic reticulum membranes; 50 ƁM SPC induces the release of 70Ő80% of the accumulated calcium. SPC releases calcium from cardiac sarcoplasmic reticulum through the ryanodine receptor, since the release is inhibited by the ryanodine receptor channel antagonists ryanodine, Ruthenium Red and sphingosine. In intact cardiac myocytes, even in the absence of extracellular calcium, SPC causes a rise in diastolic Ca2+, which is greatly reduced when the sarcoplasmic reticulum is depleted of Ca2+ by prior thapsigargin treatment. SPC action on the ryanodine receptor is Ca2+-dependent. SPC shifts to the left the Ca2+-dependence of [3H]ryanodine binding, but only at high pCa values, suggesting that SPC might increase the sensitivity to calcium of the Ca2+-induced Ca2+-release mechanism. At high calcium concentrations (pCa 4.0 or lower), where [3H]ryanodine binding is maximally stimulated, no effect of SPC is observed. We conclude that SPC releases calcium from cardiac sarcoplasmic reticulum membranes by activating the ryanodine receptor and possibly another intracellular Ca2+-release channel, the sphingolipid Ca2+-release-mediating protein of endoplasmic reticulum (SCaMPER) [Mao, Kim, Almenoff, Rudner, Kearney and Kindman (1996) Proc. Natl. Acad. Sci. U.S.A 93, 1993Ő1996], which we have identified for the first time in cardiac tissue.

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Modulation of sheep cardiac sarcoplasmic reticulum calcium-release channel open probability by ATP

Journal of Molecular and Cellular Cardiology ◽

10.1016/0022-2828(90)91587-w ◽

1990 ◽

Vol 22 ◽

pp. S20

Author(s):

Antonella Boraso ◽

Alan J Williams

Keyword(s):

Sarcoplasmic Reticulum ◽

Calcium Release ◽

Calcium Release Channel ◽

Open Probability ◽

Release Channel ◽

Cardiac Sarcoplasmic Reticulum ◽

Sarcoplasmic Reticulum Calcium

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Modulation of the Frequency of Spontaneous Sarcoplasmic Reticulum Ca2+ Release Events (Ca2+ Sparks) by Myoplasmic [Mg2+] in Frog Skeletal Muscle

The Journal of General Physiology ◽

10.1085/jgp.111.2.207 ◽

1998 ◽

Vol 111 (2) ◽

pp. 207-224 ◽

Cited By ~ 47

Author(s):

Alain Lacampagne ◽

Michael G. Klein ◽

Martin F. Schneider

Keyword(s):

Skeletal Muscle ◽

Sarcoplasmic Reticulum ◽

Calcium Release ◽

Frog Skeletal Muscle ◽

Calcium Release Channel ◽

Release Channel ◽

Event Frequency ◽

Open Time ◽

Channel Opening ◽

Sr Calcium Release

The modulation by internal free [Mg2+] of spontaneous calcium release events (Ca2+ “sparks”) from the sarcoplasmic reticulum (SR) was studied in depolarized notched frog skeletal muscle fibers using a laser scanning confocal microscope in line-scan mode (x vs. t). Over the range of [Mg2+] from 0.13 to 1.86 mM, decreasing the [Mg2+] induced an increase in the frequency of calcium release events in proportion to [Mg2+]−1.6. The change of event frequency was not due to changes in [Mg-ATP] or [ATP]. Analysis of individual SR calcium release event properties showed that the variation in event frequency induced by the change of [Mg2+] was not accompanied by any changes in the spatiotemporal spread (i.e., spatial half width or temporal half duration) of Ca2+ sparks. The increase in event frequency also had no effect on the distribution of event amplitudes. Finally, the rise time of calcium sparks was independent of the [Mg2+], indicating that the open time of the SR channel or channels underlying spontaneous calcium release events was not altered by [Mg2+] over the range tested. These results suggest that in resting skeletal fibers, [Mg2+] modulates the SR calcium release channel opening frequency by modifying the average closed time of the channel without altering the open time. A kinetic reaction scheme consistent with our results and those of bilayer and SR vesicle experiments indicates that physiological levels of resting Mg2+ may inhibit channel opening by occupying the site for calcium activation of the SR calcium release channel.

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