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Blockade of cardiac sodium channels by TTX during ischemia maintained polarized arrest, which was more protective than depolarized arrest, possibly because of reduced ionic imbalance.

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Understanding of calcium metabolism in health and disease has been retarded by the lack of an adequately sensitive bioassay of parathyroid hormone. The problem of dissociation of bioactivity and immunoactivity, well recognized for other polypeptide hormones, is exaggerated in the case of parathyroid hormone by the disproportionately long half-time in the circulation of the immunoreactive fragments. A new method of assaying the biological activity of parathyroid hormone in plasma has been developed, based on the cytochemical methods which have yielded highly sensitive bioassays of other polypeptide hormones. It depends on the stimulation of glucose 6-phosphate dehydrogenase activity in the distal convoluted tubules of segments of guinea-pig kidney maintained in vitro, and measured by microdensitometry. The limit of sensitivity of the assay is 5 fh/ml (bPTH); the index of precision is 0.09 +/- 0.04 (mean +/- SEM; n = 11).

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Esmolol at millimolar concentrations causes diastolic ventricular arrest by two mechanisms: at 1 mmol/L (and below), the pronounced negative inotropic effect is due largely to inhibition of L-type Ca(2+) channels; additionally, higher concentrations prevent action potential conduction, probably due to the inhibition of fast Na(+) channels.