Effects of high extracellular magnesium on electrophysiological properties of membranes of Retzius neurons in leech Haemopis sanguisuga

Magnesium is a bioessential cation with an important role in the function of excitable cells both in health and disease. Magnesium has therapeutic use as an anticonvulsant, anaesthetic, analgesic and antiarrhythmic agent. The aim of this work was to examine in detail the effects of high extracellular Mg2+ on the nerve cell membrane using classical electrophysiology techniques. The experiments were conducted on Retzius neurons in the isolated segmental ganglia of the leech Haemopis sanguisuga. Intracellular recording of membrane potential and electrical activity, as well as current clamp experiments to examine membrane input resistance and excitability, were performed prior to and during application of 20 mmol dm-3 MgCl2. The paper presents our findings on the effects of high Mg2+ on basic electrophysiological properties and activity of Retzius cells. Depolarization of the membrane potential, a decrease in the frequency of spontaneous activity, an increase in threshold potential, a decrease in cell excitability and an increase in input membrane resistance were found following an application of high Mg2+ solution. The underlying mechanisms of the overall suppressive action of Mg2+ on our cell model are discussed to be multiple Mg2+ effects on different ion channel conductances, with a possibly dominant blockade of Na+ channels and a probable modulation of activity of Ca2+-activated K+ channels by Mg2+.