Cardiomyocyte contraction depends on rapid changes in intracellular @entity141 . In mammals, @entity141 influx as L-type @entity141 current (ICa) triggers the release of @entity141 from sarcoplasmic reticulum (SR) and @entity141 -induced @entity141 release (CICR) is critical for excitation-contraction coupling. In fish, the relative contribution of external and internal @entity141 is unclear. Here, we characterized the role of ICa to trigger SR @entity141 release in @entity5660 ventricular myocytes using ICa regulation by @entity141 as an index of CICR. ICa was recorded with a slow (EGTA) or fast (BAPTA) @entity141 chelator in control and @entity3044 conditions. In the absence of b-adrenergic stimulation, the rate of ICa inactivation was not significantly different in EGTA and @entity18650 (27.1    1.8 vs. 30.3    2.4 ms), whereas with @entity3044 (1  M), inactivation was significantly faster with EGTA (11.6    1.7 vs. 27.3    1.6 ms). When barium was the charge carrier, inactivation was significantly slower in both conditions (61.9    6.1 vs. 68.0    8.7 ms, control, @entity3044 ). Quantification revealed that without @entity3044 , only 39% of ICa inactivation was due to @entity141 , while with @entity3044 , inactivation was @entity141 -dependent (   65%) and highly reliant on SR @entity141 (   46%). Thus, SR @entity141 is not released in basal conditions, and ICa is the main trigger of contraction, whereas during a stress response, SR @entity141 is an important source of cytosolic @entity141 . This was not attributed to differences in SR @entity141 load because @entity5834 -induced transients were not different in both conditions. Therefore, @entity141 stored in SR of trout cardiomyocytes may act as a safety mechanism, allowing greater contraction when higher contractility is required, such as stress or exercise.

The calcium stored in the sarcoplasmic reticulum acts as a safety mechanism in XXXX heart.

@entity5660 :: ('8022', 'Species') :: ['rainbow trout'] @entity5834 :: ('MESH:D002110', 'Chemical') :: ['caffeine'] @entity3044 :: ('MESH:D007545', 'Chemical') :: ['isoproterenol'] @entity18650 :: ('MESH:C025603', 'Chemical') :: ['BAPTA'] @entity141 :: ('CHEBI:29108', 'Chemical') :: ['Ca(2+)']
@entity5660 :: (8022,Species) :: ['rainbow trout']
