Effects of hyperpolarizing pulses on a cardiac pacemaker cell

The authors' mathematical model of a rabbit sinoatrial node (SAN) cell (see S. Demir et al., Amer. J. Physiol., vol. 266, p. C832-52, 1994) was studied to explain the phase-sensitive response of this pacemaker cell to single and periodic pulses of hyperpolarizing electrical current. The resulting simulations were presented in phase response curves (PRCs) for the single pulse and in entrainment curves (ECs) for the periodically applied pulses. These graphical representations provided quantitative description of the phase-sensitivity behavior of the SAN cell in rabbit. The authors' computations showed that the characteristics of the phase-sensitive effects are dependent upon the intensity of the stimulus applied. Current-voltage (IV) analysis concluded that the action potential threshold determined by I/sub Ca,L/ was not affected by electrical perturbations. The changes in I/sub Na,Ca/, I/sub f/, I/sub Na/ and I/sub Ca,T/ currents during diastole determine the rate of diastolic depolarization which results in delaying or advancing the following action potential after a stimulus is applied.