ISSN:
1432-1424
Keywords:
Ca2+-release channels
;
Sarcoplasmic reticulum
;
Cardiac
;
Sulmazole
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract We investigated the effects of changes in luminal [Ca2+] on the gating of native andpurified sheep cardiac sarcoplasmic reticulum (SR) Ca2+-release channels reconstituted intoplanar phospholipid bilayers. The open probability (P o )of channels activated solely by cytosolic Ca2+ was greater at positive than negative holding potentials. Channels activatedsolely by 10 μm cytosolic Ca2+ exhibited no change in steady-stateP o or in the relationship betweenP o and voltage when the luminal[Ca2+] was increased from nanomolar to millimolar concentrations. In the absence of activating concentrationsof cytosolic Ca2+, the channel can be activated by the phosphodiesterase inhibitor sulmazole (AR-L 115BS). However, cytosolicCa2+-independent activation of the channel by sulmazole requires luminal Ca2+. In the presence ofsulmazole, at picomolar luminal [Ca2+] the channel remains completely closed. Increasing the luminal [Ca2+]to millimolar levels markedly increases the P o via an increase in theduration of open events. The P o and duration of the sulmazole-activated, luminalCa2+-dependent channel openings are voltage dependent. In the presence of micromolar luminal Ca2+, theP o and duration of sulmazole-activated openings are greater atnegative voltages. However, at millimolar luminal [Ca2+], long openings are also observed at positive voltages and theP o appears to be similar at positive and negative voltages. Our findings indicate thatthe regulation of channel gating by luminal Ca2+ depends on the mechanism of channel activation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00232590
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