Objective To investigate properties of electrophysiology and effects of ouabain on transient outward potassium current (Ito) and L-type calcium current (ICa-L) of left atrium posterior wall (LAPW) and left atrium appendage tissue (LAA) of rabbit, it could provide the scientific explanations that LAPW and ouabain could enhance atrial fibrillation (AF) vulnerability via increasing electrophysiological heterogeneity and electrical remodelling of different region of left atrium in rabbits.
Methods Atrial myocytes coming from LAPWs and LAAs of rabbits perfused via vitro heart perfusion system were obtained by enzymatic dissociation. The whole-cell patch-clamp technique was used to assess effects of ouabain on Ito and ICa-L. The current-voltage (I-V) curves of Ito and ICa-L on LAPW and LAA myocytes were fitted before and after of ouabain administration.
Results (1) With holding potential −50 mV and commanding potential +50mV, the current densities of LAPW Ito were decreased slightly less than that of LAA Ito in control groups in control groups (p>0.05). After administration of ouabain. the current densities of LAPW Ito were significantly larger than that of LAA Ito ((10.97±0.58) pA/pF vs (9.39±0.83) pA/pF, p<0.05, respectively). The I∼V curve of LAPW Ito was gently lowered to I∼V curve of LAA Ito in control groups. But with perfusion of ouabain, the I∼V curve of LAPW Ito opposed to I∼V curve of LAA Ito was significantly changed from the bottom to the top with same upward direction. (2) At voltage clamp protocol of ICa-L, the current densities of LAPW ICa-L were markedly decreased compared with that of LAA ICa-L in control groups (p<0.05). With the addition to ouabain, the peak of amplitude of LAPW ICa-L at +20 mV was obviously increased to that of LAA ICa-L ((−11.13±0.99) pA/pF vs (−8.86±0.51) pA/pF, p<0.01, respectively). At the control groups, the I∼V curve of LAPW ICa-L was arranged the bottom of all I∼V curves of ICa-L. The I∼V curve of LAPW ICa-L, but through effects of ouabain, was completely upgraded to the top of other I∼V curves of ICa-L. However, all shapes and directions of current peak of I∼V curves of ICa-L were not changed between the control group and ouabain groups.
Conclusion The distribution properties of ICa-L have significant difference on LAPW of rabbit. Ouabain could accentuate the electrophysiological heterogeneity and electrical remodelling of Ito and ICa-L in LAPW of rabbits. It might contribute trigger and persistence factors to AF vulnerability.