Regional differences in rabbit atrial repolarization: importance of transient outward current

Abstract

Regional differences in rabbit atrial repolarization were investigated using a conventional microelectrode technique. A more rapid phase 1 repolarization (lower phase 1 amplitude) was seen in the left atrial (LA) roof area compared with the right atrial (RA) roof area: 54 +/- 10 vs. 82 +/- 6 mV at 1,000 ms (P < 0.001). In addition, action potential duration at 40 mV above the resting potential (APD40) was shorter in LA and was associated with a slower phase 3 repolarization rate. Furthermore, the recovery time constant of phase 1 amplitude at 500 ms was 0.9 +/- 0.2 s in LA and 3.5 +/- 1.5 s in RA (P < 0.001). Pacing cycle lengths (2,000, 1,500, 1,000, 800, and 500 ms) modulated phase 1 amplitude, APD40, and phase 3 rate in both regions. 4-Aminopyridine (4-AP; 1 mM), a selective transient outward current (I(to)) blocker, abolished cycle length dependence of the above action potential parameters and diminished the differences in electrophysiological properties between the two regions. 4-AP also flattened the restitution curve of phase 1 amplitude in both regions. In conclusion, the findings suggest that the different kinetics of I(to) play an important role in regional differences of atrial repolarization.

Comparison of time- and voltage-dependent K+ currents in myocytes from left and right atria of adult mice

“…Previous descriptions of I to in mouse atrium (48) did not draw attention to this. Regional heterogeneity of I to amplitude within left and right atria has been demonstrated in guinea pig (45), rabbit (33,49), and dog (9). We suggest that regional heterogeneity of I to expression within adult mouse atria may account for the range of I to amplitudes in our data.…”

“…Our results show that the left atrium of the mouse has a shorter ERP than the right atrium. Previous electrophysiological studies (19,20,33,34,46,47) on many other mammals, including dogs, rabbits, pigs, and goats, have revealed this same trend. Thus it appears that in several mammalian species the left atrium, which is depolarized after the right atrium, repolarizes more quickly than the right atrium.…”

“…Previous electrophysiological studies (19,20,33,34,46,47) on other mammals, including dogs, rabbits, pigs, and goats, have revealed that the left atrium repolarizes more quickly than the right atrium. How- current recorded at ϩ45 mV after an inactivating prepulse protocol.…”

“…Interatrial differences in refractoriness have also been described. The effective refractory period (ERP) of the left atrium is shorter than that of the right atrium in dogs (20), rabbits (33,34), pigs (47), and goats (46).…”

Characterization and Comparison of Na^&plus;, K^&plus; and Ca^2&plus; Currents Between Myocytes from Human Atrial Right Appendage and Atrial Septum

“…The heterogeneity of electrophysiology in the heart has long been recognized as a critical determinant of normal cardiac function and abnormally enhanced spatial dispersion of repolarization however plays a significant role in arrhythmogenesis [1,2,[10][11][12][13]. Regional differences in repolarization and the underlying ionic currents between left and right atria [14], between the crista terminalis and pectinate muscles [15], and even within the right atrium [11], have been well documented and these differences are believed to contribute to the occurrence of AF [1,2,[10][11][12][13]. Action potential variations between the right and left atrial roofs [14] or between the crista terminalis and pectinate muscles [15] in rabbit seem to involve in differences of transient outward K + current (I to ).…”