The effects of intercellular coupling conductance on the activity of two electrically coupled isolated rabbit sinoatrial nodal cells were investigated. A computer-controlled version of the “coupling clamp” technique was used in which isolated sinoatrial nodal cells, not physically in contact with each other, were electrically coupled at various values of ohmic coupling conductance, mimicking the effects of mutual interaction by electrical coupling through gap junctional channels. We demonstrate the existence of four types of electrical behavior of coupled spontaneously active cells. As the coupling conductance is progressively increased, the cells exhibit: (a) independent pacemaking at low coupling conductances, (b) complex dynamics of activity with mutual interactions, (c) entrainment of action potential frequency at a 1:1 ratio with different action potential waveforms, and (d) entrainment of action potentials at the same frequency of activation and virtually identical action potential waveforms. The critical value of coupling conductance required for 1:1 frequency entrainment was <0.5 nS in each of the five cell pairs studied. The common interbeat interval at a relatively high coupling conductance (10 nS), which is sufficient to produce entrainment of frequency and also identical action potential waveforms, is determined most by the intrinsically faster pacemaker cell and it can be predicted from the diastolic depolarization times of both cells. Evidence is provided that, at low coupling conductances, mutual pacemaker synchronization results mainly from the phase-resetting effects of the action potential of one cell on the depolarization phase of the other. At high coupling conductances, the tonic, diastolic interactions become more important.
Pacemaker Synchronization of Electrically Coupled Rabbit Sinoatrial Node Cells
Address correspondence to Dr. E. Etienne Verheijck, Academic Medical Center, University of Amsterdam, Department of Physiology, PO Box 22700, 1100 DE Amsterdam, The Netherlands. Fax: 31 20 6919319; E-mail: [email protected]
Abbreviations used in this paper: APD50, action potential duration at 50% repolarization; DDR, diastolic depolarization rate; DDT, diastolic depolarization time; Gc, coupling conductance; IBI, interbeat interval; Ic, coupling current; Icap, capacitative current; Iion, membrane ionic current; KB, Kraft-Brühe; SA, sinoatrial.
E. Etienne Verheijck, Ronald Wilders, Ronald W. Joyner, David A. Golod, Rajiv Kumar, Habo J. Jongsma, Lennart N. Bouman, Antoni C.G. van Ginneken; Pacemaker Synchronization of Electrically Coupled Rabbit Sinoatrial Node Cells . J Gen Physiol 1 January 1998; 111 (1): 95–112. doi: https://doi.org/10.1085/jgp.111.1.95
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