Parathyroid hormone stimulates calcium influx and the cAMP messenger system in rat enterocytes

Direct effects of parathyroid hormone (PTH) on calcium uptake byisolated rat duodenal cell preparations enriched in enterocytes wereinvestigated. PTH significantly stimulated enterocyte⁴⁵Ca²⁺influx in a time-dependent (1-10 min) manner and at all doses tested (2 × 10¹³ to10⁷ M). TheCa²⁺ channel antagonists verapamil(10 µM) and nitrendipine (1 µM) completely blocked the stimulationof Ca²⁺ influx by the hormone(10⁸ M). PTH markedlyincreased cAMP levels in rat duodenal cells (88, 167, and 67%, after1, 2, and 3 min, respectively). In agreement with these observations,forskolin (adenylate cyclase activator), dibutyryl adenosine3',5'-cyclic monophosphate (DBcAMP), and Sp-cAMPS (cAMPanalogs) mimicked, whereas Rp-cAMPS (cAMP antagonist) suppressed PTHand DBcAMP activation of enterocyte calcium uptake. Furthermore, theeffects of DBcAMP were abolished by nitrendipine. These results showdirect rapid effects of PTH on duodenal cells'Ca²⁺ influx, which involve theactivation of a dihydropyridine-sensitive Ca²⁺ influx pathway and the cAMPsecond messenger system.