Effects of barium on mature and embryonic heart cells.

• The effect of barium ion on the electrical and mechanical activity of the heart has been reported by many investigators." The production of various degrees of heartblock, idioventricular rhythm, extrasystoles, tachycardia and fibrillation have been observed." Boehm noted in 1875 that the barium ion in small doses, 10 to 30 mg/kg, increased the work of the frog's heart without changing its frequency and that relatively large doses, 50 to 100 mg/kg, given subcutaneously, produced irregularities and cardiac arrest. Kruta observed that barium can initiate automatic activity in quiescent strips of mammalian left atrium. The same effect has also been observed in quiescent strips of frog ventricle/"' By means of intracellular glass capillary electrodes Kleinfeld et al. observed that the transmembrane action potentials recorded from the apical strip of frog ventricle showed depolarization during diastole and slowing of repolarization. The amplitude of the transmembrane action potential was unchanged. Since this region of the ventricle is devoid of ganglia and nervous connections, it was concluded that barium can initiate automaticity and that it has a myogenic action. More recently it has been shown by Lehmkuhl and Sperelakis that barium administered to embryonic chick heart cells initiates pacemaker activity in heart cells previously quiescent.