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G Picotto

Publications and source records attributed to G Picotto.

8 recordsLinked to original sources
PubMed2001

Rapid effects of calciotropic hormones on female rat enterocytes: combined actions of 1,25(OH)2-vitamin D3, PTH and 17beta-estradiol on intracellular Ca2+ regulation.

1,25(OH)(2)-Vitamin D(3) [1,25(OH)(2)D(3)], PTH and 17beta-estradiol increase intracellular Ca(2+) levels ([Ca(2+)](i)) in rat enterocytes by stimulating inner Ca(2+) store mobilization and voltage-dependent Ca(2+) channels through non-genomic activation of second-messenger cascades. The participation of store-operated Ca(2+) (SOC) channels in 17beta-estradiol regulation of enterocyte [Ca(2+)](i) has also been suggested. The aim of this work was to investigate whether PTH and/or 17beta-estradiol exert additive or synergistic effects acting in concert with the classic intestinal calciotropic hormone 1,25(OH)(2)D(3). Fura-2-loaded rat duodenal cells were stimulated using rPTH (10 nM), 17beta-estradiol (0.1 nM) or 1,25(OH)(2)D(3) (0.1 nM). The resulting Ca(2+) signal was characterized by an almost immediate rise in [Ca(2+)](i) (within 30 s) rapidly reaching peak levels, followed by a plateau phase that remained sustained as long as the cells were exposed to the stimulus. The addition of PTH at the sustained phase induced by 1,25(OH)(2)D(3) or, conversely, the addition of the secosteroid after the PTH-induced effect, did not induce additional increases in [Ca(2+)](i). Simultaneous treatment with both hormones resulted in an elevation of [Ca(2+)](i) equivalent to the maximal level caused by either agonist alone, suggesting common components for [Ca(2+)]i stimulation by PTH and 1,25(OH)(2)D(3). Treatment with 17beta-estradiol at the sustained phase induced by 1,25(OH)(2)D(3) or, conversely, treatment with the secosteroid after the 17beta-estradiol effect, induced additional increments in [Ca(2+)](i) (58 % and 63 %, respectively). Simultaneous treatment of enterocytes with both steroids potentiated their individual effects to the same extent as when added sequentially, also indicative of additive actions mediated by different sources of calcium signaling cascades. Moreover, 17beta-estradiol failed to further increase the 1,25(OH)(2)D(3)-induced initial Ca(2+) elevation in Ca(2+)-free medium, thus suggesting that extracellular influx mechanisms rather than intracellular Ca(2+) mobilization account for estrogen potentiation of 1,25(OH)(2)D(3) modulation of [Ca(2+)](i) in duodenal cells.

Animals↗
PubMed2000

Effect of aging on the mechanisms of PTH-induced calcium influx in rat intestinal cells.

We have investigated the effects of aging on parathyroid hormone (PTH) modulation of intracellular calcium homeostasis and their relationship to signal transduction pathways in isolated rat duodenal cells (enterocytes). PTH (10(-8)-10(-9) M) increased enterocyte (45)Ca(2+) influx and intracellular Ca(2+) concentration ([Ca(2+)](i)) to a greater extent (twofold and 50%, respectively) in aged (24 months) than in young (3 months) animals. The [Ca(2+)](i) response of old cells to the hormone was slower, lacking the early phase of changes in cytosolic Ca(2+). Ca(2+) influx induced by PTH was prevented by the protein kinase A antagonist Rp-cAMPS in both young and aged enterocytes, whereas neomycin and compound U73122, inhibitors of PLC-catalyzed phosphoinositide hydrolysis, abolished hormone-dependent Ca(2+) influx in young but had no effect on aged cells. Higher basal adenylyl cyclase (AC) activity and cAMP content were detected in old enterocytes. PTH increased the absolute levels of cAMP in aged cells and AC activity of microsomes isolated therefrom to a greater extent (>/= twofold) than in young enterocytes/membranes. In young cells, the hormone also induced a rapid and transient release of inositoltrisphosphate (IP(3)) and diacylglycerol (neomycin-sensitive) at 45 sec, and a delayed phase of DAG at 5 min (neomycin-insensitive). The early formation of IP(3) and DAG was blunted in aged animals. These results suggest that both the PLC and adenylyl cyclase cascades are involved in PTH stimulation of Ca(2+) influx in duodenal cells. During aging, however, only the cAMP pathway is operative, mediating a potentiation of the effects of the hormone. Additional studies are required to establish the relative role of PTH-dependent messenger systems in the regulation of intestinal calcium absorption and age-related abnormalities.

Adenylyl Cyclases↗
PubMed1999

17beta-oestradiol increases intracellular Ca2+ concentration in rat enterocytes. Potential role of phospholipase C-dependent store-operated Ca2+ influx.

The involvement of the phospholipase C (PLC) pathway in the non-genomic regulation of duodenal cell Ca2+ concentration by 17beta-oestradiol was investigated. The PLC inhibitors neomycin (0.5 mM) and U-73122 (2 microM) suppressed the stimulatory effect of 0.1 nM 17beta-oestradiol on the 45Ca2+ influx into enterocytes isolated from rat duodenum. The hormone (1 pM to 10 nM) increased the formation of 1,2-diacylglycerol in a biphasic pattern, characterized by an early peak at 45 s (+82%) and a later peak at 5 min (+46%). Both PLC inhibitors suppressed the first peak but were unable to block the 17beta-oestradiol effect at 5 min. 17beta-Oestradiol also increased the generation of inositol 1,4,5-trisphosphate within 15 s, with maximal stimulation at 30 s. 17beta-Oestradiol induced a rapid (30 s) and sustained (up to 5 min) increase in the intracellular Ca2+ concentration ([Ca2+]i) of fura 2-loaded enterocytes. The fast rise in [Ca2+]i was specific because other sex steroid hormones were without effect and could be blocked to a great extent by U-73122 (by 86% at 1 min). The effects of 17beta-oestradiol on enterocyte [Ca2+]i were decreased significantly (by 75%) in a Ca2+-free extracellular medium but a pronounced increase in [Ca2+]i was obtained after readmission of Ca2+ to the medium. The latter change was suppressed by 10 microM La3+, whereas nitrendipine (1 microM) and verapamil (10 microM) separately were without effect. The permeability of the 17beta-oestradiol-induced Ca2+ influx pathway to Mn2+ was increased 2.8-fold by treatment with oestrogen. These results suggest the operation of a PLC-dependent store-operated Ca2+ channel mechanism in 17beta-oestradiol regulation of enterocyte extracellular Ca2+ influx.

Animals↗
PubMed1997

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

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 x 10(-13) to 10(-7) M). The Ca2+ channel antagonists verapamil (10 microM) and nitrendipine (1 microM) 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.

Adenylyl Cyclases↗
PubMed1996

Acute stimulation of intestinal cell calcium influx induced by 17 beta-estradiol via the cAMP messenger system.

Recent studies have provided evidence for nuclear estrogen receptor-mediated calcium transport in intestinal mucosal cells. The possibility that, in addition, estrogens directly stimulate intestinal Ca2+ fluxes through second-messenger pathways was investigated. Exposure of enterocytes isolated from female rat duodenum to low physiological levels of 17 beta-estradiol (10(-11), 10(-10) and 10(-8) M) rapidly (1-10 min) increased (50-170%) cell 45Ca2+ influx. 17 alpha-Estradiol, dihydrotestosterone and progesterone were devoid of activity, suggesting specificity of the estrogen effect. Maximum responses induced by 17 beta-estradiol (5 min at 10(-10) M) could be abolished to a great extent (84%) by pretreating the cells with verapamil (10 microM) and nitrendipine (1 microM), involving the activation of voltage-dependent Ca2+ channels in the fast increase of rat duodenal calcium uptake by the hormone. Evidence was obtained indicating that the acute estrogen stimulation of enterocyte Ca2+ influx is mediated by the cyclic AMP/PKA pathway. 17 beta-Estradiol rapidly increased cAMP content of rat duodenal cells in parallel to the changes in Ca2+ uptake. In addition, forskolin, dibutyryl cAMP and Sp-cAMPS mimicked and Rp-cAMPS suppressed the prompt 17 beta-estradiol-induced stimulation of Ca2+ influx. These results are consistent with a direct action of estrogens in the enterocyte, presumably a non-genomic one, initiated on the cell surface and resulting in rapid activation of the cAMP pathway and Ca2+ channels, which may be relevant for regulation of intestinal calcium transport.

Adenylyl Cyclases↗