COMPUTER-SIMULATION OF THE ELECTROTONIC MODULATION OF PACEMAKER ACTIVITY IN THE SINOATRIAL NODE BY ATRIAL MUSCLE

Electrotonic interaction between the sinoatrial (SA) node and surround ing atrial muscle was investigated in a computer simulation using a mo dified Oxsoft HEART model (Oxsoft, Oxford, UK). When an SA node cell m odel was coupled to a passive atrial membrane model (RC circuit) with various coupling conductances (G(c)), there was a G(c)-dependent prolo ngation of spontaneous cycle length (SCL). At a sufficiently high valu e of G(c), the spontaneous activity was finally stopped. A nonlinear r elationship between G(c) and SCL was obtained, similar to that observe d in experiments on rabbit SA node cells. When the muscarinic potassiu m current (i(K,ACh)) was activated in the SA node cell model, the coup ling-induced inhibition of pacemaker activity was potentiated. Althoug h coupling current and i(K,ACh) were additive, their effects on SCL we re more than additive because of the nonlinear dependence of SCL on ne t current. A decrease in the input resistance of the atrial membrane m odel to simulate the activation of i(K,ACh) in atrial muscle was also shown to potentiate the coupling-induced inhibition of SA node spontan eous activity.