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In earlier investigations it has been found that high arterial blood pressure of salt-sensitive DAHL rats (DAHL-S) that received a diet containing 8% NaCl could be normalized by chronic treatment with specific calcium antagonists, as for instance, nitrendipine or anipamil. Parallel measurements on heart and arterial vasculature with atomic absorption spectrometry revealed that there was a rise in absolute calcium content upon development of hypertension, whereas under the influence of nitrendipine, not only the blood pressure and heart weight but also myocardial (and arterial) tissue calcium content remained in the physiologic range. In the present study, an additional determination of the free intracellular calcium ion concentration with Ca-sensitive microelectrodes was carried out. For technical reasons, the measurements were restricted to isolated resting rat papillary muscles (stretched to optimal length in a perfusion bath of 1.5 ml at 30 degrees C in normal Tyrode solution). The impalement of the electrodes was considered adequate when the heights of Ca potential and membrane potential were constant for more than twenty minutes. In order to produce severe systemic hypertension, a group of six-week-old DAHL-S rats was fed with an 8% NaCl diet over five weeks. Another group of DAHL-S rats received additionally 150 mg/kg nitrendipine twice a day orally. Salt-resistant DAHL-R rats, also fed with an 8% NaCl diet, served as controls. The findings of this preliminary study are as follows (n = 5 in each group): (table; see text).

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