Antagonistische Wirkungen von Magnesium-, Calcium-und Natriumionen auf die Impulsbildung im Sinusknoten des Meerschweinchenherzens

Abstract

The mutual actions of magnesium, calcium and sodium ions on spontaneous impuls generation of isolated guinea-pig atria were investigated. Atria suspended in magnesiumfree bicarbonate buffered solution containing only 0.08 mM calcium exhibit a high, sometimes irregular spontaneous activity. A stepwise addition of calciumchloride leads to 3 characteristic changes in steady state beat interval (s.s.b.i.): increase in s.s.b.i., maximum at 0.31–0.62 mM calcium, then a decrease in s.s.b.i., minimum at 5–10 mM calcium, and then again an increase in s.s.b.i. up to a concentration of 15 mM calcium. The possible role of neurotransmittors in mediating this chronotropic effects was excluded by use of specific antagonists, atropin (1 mg/l) and pronethalol (1 and 5 mg/l).