Rate of active tension development from rigor in skinned atrial and ventricular cardiac fibres from @entity1707 following photolytic release of @entity855 from caged XXXX .

@entity1707 @entity141 @entity855 @entity13143 @entity2701 @entity73144
We investigated the rate of tension development (kappa td) after photolytical release of @entity855 from @entity73144 ('caged @entity855 ') of atrial and ventricular fibre bundles from @entity1707 . Contraction was initiated from @entity2701 ( @entity2701 ) and low-tension (LT) rigor at maximal @entity141 activation (pCa 4.5). The kappa td of atrial fibre bundles was 6.8 s-1 from LT and 6.9 s-1 from @entity2701 rigor. Rate of tension development of ventricular fibre bundles was significantly lower (P < 0.001) being 1.06 s-1 and 0.94 s-1 from LT and @entity2701 rigor, respectively. The kappa td of skinned ventricular fibre bundles incubated in a high [K+], low [ @entity141 ] (cardioplegic) solution prior to the skinning procedure decreased significantly (P < 0.05) to 0.73 s-1 and 0.63 s-1 from LT and @entity2701 rigor, respectively, whereas that of skinned atrial fibre bundles remained at 7.1 s-1 and 6.9 s-1 from LT and @entity2701 rigor, respectively. Phosphorylation levels of the @entity13143 light chain 2 isoform in the atrial fibre bundles (ALC-2) was 15.6 +/- 2.7%. The corresponding values for the two ventricular isoforms, VLC-2 and VLC-2*, were 31.2 +/- 0.4% and 25.1 +/- 2.1%, respectively. Phosphorylation levels of fibre bundles incubated in cardioplegic solution prior to skinning were 11.6%, 18.9%, and 15.4% of the ALC-2, VLC-2 and VLC-2*, respectively. The results show that the rate of tension development is more than seven-fold higher in the atrial compared with ventricular fibre bundles. These results correlate with the differences in ATPase activity of the contractile proteins in solution and, most likely, reflect differences in the @entity13143 isoform composition. In ventricular fibre bundles the increased levels of light chain phosphorylation were associated with increased rate of contraction.
