XXXX releases calcium from sarcoplasmic reticulum in calcium-tolerant @entity35 cardiac myocytes.

@entity35 @entity8452 @entity4527 @entity5834 @entity6028 @entity1360 @entity141
1. The hypothesis tested in this study is that @entity8452 depletes sarcoplasmic reticulum (s.r.) @entity141 loading in suspensions of single adult @entity35 cardiac myocytes by effecting @entity141 release into the myoplasm resulting in an increase in myoplasmic free [ @entity141 ] ([ @entity141 ]i). The latter was monitored by the fluorescent dye, @entity6028 . 2. The competency of the technique to detect s.r. @entity141 release was tested by using @entity5834 to induce @entity141 release. The addition of 5-10 mM- @entity5834 to myocytes loaded with @entity6028 and incubated in a medium containing 1 mM- @entity141 gives a large, transient increase in fluorescence, which is interpreted as indicating an increase in [ @entity141 ]i. If the chelating agent @entity4527 is added to the cell suspension 1-5 min prior to the @entity5834 , to a concentration sufficient to decrease extracellular @entity141 to 0.1-0.15 microM, then @entity5834 again gives a large, transient increase in fluorescence, indicative of the fact that sarcolemmal @entity141 transport is not necessary for this response. The ionophore @entity1360 also raises [ @entity141 ]i in a transient manner when added after EGTA. The addition of @entity5834 prior to @entity1360 largely diminishes the response to the latter; however, addition of @entity1360 prior to @entity5834 totally abolishes its effect to increase [ @entity141 ]i. This is taken to indicate that the intracellular store which is releasable by @entity5834 --and which presumably reflects the s.r.--is also releasable by @entity1360 : @entity1360 , however, also gives access to another, minor intracellular pool. 3. The plant alkaloid, @entity8452 , at concentrations of 10(-8) to 10(-6) M, consistently causes a slow and prolonged increase in [ @entity141 ]i when added to cell suspensions incubated with 1 mM-extracellular @entity141 . Under conditions precluding net entry of @entity141 into the cell, viz. 0.1 microM-extracellular @entity141 , @entity8452 causes a more limited, partially reversible, increase in [ @entity141 ]i. 4. When added prior to EGTA, @entity8452 attenuates, or prevents, the subsequent response to @entity5834 : efficacy depends upon the time of pre-incubation (1-10 min) and the concentration of @entity8452 (10(-8) to 10(-6) M). When the response to @entity5834 is largely prevented by @entity8452 , the response to @entity1360 is also severely attenuated, i.e. there is no evidence that @entity8452 causes sequestration of @entity141 within an @entity1360 -sensitive pool.(ABSTRACT TRUNCATED AT 400 WORDS)
