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Vol. 273, Issue 4, C1349-C1353, October 1997
Departamento de Biología, Bioquímica, y Farmacia, Universidad Nacional del Sur, 8000 Bahía Blanca, Argentina
Direct effects of parathyroid hormone (PTH) on calcium uptake by
isolated rat duodenal cell preparations enriched in enterocytes were
investigated. PTH significantly stimulated enterocyte
45Ca2+
influx in a time-dependent (1-10 min) manner and at all doses tested (2 × 10
13 to
10
7 M). The
Ca2+ channel antagonists verapamil
(10 µM) and nitrendipine (1 µM) completely blocked the stimulation
of Ca2+ influx by the hormone
(10
8 M). PTH markedly
increased cAMP levels in rat duodenal cells (88, 167, and 67%, after
1, 2, and 3 min, respectively). In agreement with these observations,
forskolin (adenylate cyclase activator), dibutyryl adenosine
3',5'-cyclic monophosphate (DBcAMP), and Sp-cAMPS (cAMP
analogs) mimicked, whereas Rp-cAMPS (cAMP antagonist) suppressed PTH
and DBcAMP activation of enterocyte calcium uptake. Furthermore, the
effects of DBcAMP were abolished by nitrendipine. These results show
direct rapid effects of PTH on duodenal cells'
Ca2+ influx, which involve the
activation of a dihydropyridine-sensitive Ca2+ influx pathway and the cAMP
second messenger system.
intestine; nongenomic effects; calcium channels; adenosine 3',5'-cyclic monophosphate signaling pathway
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