Magnesium as the regulator of electrical activity in rabbit sinoatrial node cells treated with ouabain.

Recent advances in the understanding of the role of magnesium (Mg2+) as a regulator of electrical activity in sinoatrial node cells are discussed. In the presence of 10 microM ouabain or in the absence of extracellular potassium (K+), spontaneous pacemaker activity ceased rapidly. Further reduction of extracellular calcium (Ca2+) produced a rhythmic activity. The slow regenerative potential (SRP) has been used to define the rhythmic activity. To determine the ionic mechanism of inducing SRP, the effects of blocker of an inward sodium (Na+) current mediated through Ca2+ channels, Mg2+ at 5.2 mM, were studied in a preparation of rabbit sinoatrial node. The increase in extracellular Mg2+ completely blocked the SRP. In conclusion, it is suggested that the slow inward Na+ current is the most important factor for the generation of the SRP depolarization and that Mg2+ is a major extracellular regulator of the SRP.