Effects of Calcium Channel Modulators on the Regulation of Cytoplasmic Ca2+and Hormone Secretion of Parathyroid Cells

Abstract
Effects of Ca2+‐channel modulators were examined in human, bovine and murine parathyroid tissue. In 0.5 mM external Ca2+, 100 μM verapamil inhibited parathyroid hormone release, stimulated uptake and efflux of45Ca and raised cytoplasmic Ca2+concentration ([Ca2+]i). However, in 3.0 mM Ca2+the drug only affected efflux. Methoxyverapamil (50 μM) inhibited parathyroid hormone release in 0.5 mM but stimulated secretion in 3.0 mM Ca2+. BAY K. 8644 (10 μM) had similar actions as verapamil on parathyroid hormone release and [Ca2+]i, whereas nifedipine (1μM) and diltiazem (50‐100 μM) lacked effects. Despite the lack of voltage‐dependent Ca2+channels in parathyroid cells, drugs with established actions on such channels affect [Ca2+]iand parathyroid hormone release. However, these actions are not sufficiently pronounced and tissue specific to allow their use for correcting hyperparathyroidism.

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