On the mechanism of barium induced diastolic depolarisation in isolated ventricular myocytes

Barium can induce spontaneous activity in cardiac non-pacemaker cells. The mechanism of barium induced diastolic depolarisation was studied in isolated ventricular myocytes, using a microelectrode technique. Barium (0.05-0.2 mmol.litre-1) decreased resting potential and caused the membrane potential at the end of the action potential to undershoot the diminished resting value temporarily, thereby inducing diastolic depolarisation. Resting membrane resistance was increased by Ba but at the end of phase 3 repolarisation the resistance temporarily decreased below its steady state diastolic value. In presence of Ba, hyperpolarisation abolished or reversed diastolic depolarisation. At the end of phase 3 repolarisation, membrane resistance was decreased, whether diastolic depolarisation was present, absent or reversed. A high [K]o (15.4 mmol.litre-1) decreased Ba effects on action potential, membrane resistance and diastolic depolarisation. Caesium decreased the Ba induced diastolic depolarisation and the associated increase in membrane resistance, but had little effect on spontaneous activity at depolarised levels. Barium induced an oscillatory potential, with increased membrane resistance. Noradrenaline plus low [Ba]o, and high [Ba]o alone (1-5 mmol.litre-1), can induce spontaneous activity. Thus, in myocardial cells barium induces diastolic depolarisation at polarised levels by a voltage and time dependent block of potassium conductance, which is modulated by action potential voltage changes. However, as [Ba]o is increased, spontaneous activity at a depolarised level may be related to the decay of potassium currents and to oscillatory potentials.     

FM sonography in diffuse liver disease: prospective assessment and blinded analysis

FM sonography - a signal-processing technique that uses frequency and phase information as well as amplitude data - shows promise in evaluation of patients with diffuse liver disease. In a prospective blinded review of 37 patients with biopsy-proved liver disease and 42 healthy volunteers, FM sonography was clearly superior to traditional amplitude-based (AM) sonography in distinguishing healthy from diseased subjects. Statistically significant differences were seen in accuracy (FM, 98.7%; AM, 84.8%), sensitivity (FM, 97.3%; AM, 70.3%), and negative predictive value (FM, 97.7%; AM, 78.8%). Our data also suggest that current FM sonographic techniques cannot differentiate among histologic findings associated with different hepatic parenchymal abnormalities. It is unclear, therefore, whether FM imaging can reduce the numbers of patients who require biopsy for diagnosis or the frequency of biopsy procedures in patients with known disease.