Abstract
Experimental and clinical evidence suggests an important role for the intraatrial septum (IAS) in the atrial fibrillation (AF) of the vagal origin. The muscarinic K+ channel (IK,ACh) represents a relevant target for the action of vagal neurotransmitter acetylcholine (ACh) and its activation should be involved in the alterations of electrical activity in atria associated with an elevation of the vagal tone. In the present study we examined the distribution of IK,ACh in different regions of guinea-pig atria. Atrial myocytes were isolated from right atrial appendage (RAA), right atrial free wall (RA), IAS, left atrial appendage (LAA) and left atrial free wall (LA) and were voltage-clamped using the whole-cell patch-clamp technique. IK,ACh was maximally activated by 10 μM ACh at a holding potential of –40 mV and the current density of IK,ACh was estimated by normalizing the amplitude of the outward shift in the holding current with reference to the cell membrane capacitance. The densities of IK,ACh in RAA, RA, IAS, LAA and LA were 29.8±6.9 (n = 4), 31.1±2.7 (n = 5), 16.0±1.9 (n = 5), 13.5±2.3 (n = 6) and 20.8±3.0 (n = 5) pA/pF respectively. Thus, the distribution of IK,ACh in IAS is significantly smaller compared with that in RAA (P<0.05) or RA (P<0.01). These regional differences in IK,ACh density may contribute at least partly to the inhomogeneity in repolarization process in atria involved in the vagally-induced AF. [Jpn J Physiol 54 Suppl:S107 (2004)]
