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Biomedical subjects

S M Pasquale

Publications and source records attributed to S M Pasquale.

7 recordsLinked to original sources
PubMed1991

Free fatty acid accumulation in secretagogue-stimulated pancreatic islets and effects of arachidonate on depolarization-induced insulin secretion.

Free fatty acids in isolated pancreatic islets have been quantified by gas chromatography-mass spectrometry after stimulation with insulin secretagogues. The fuel secretagogue D-glucose has been found to induce little change in islet palmitate levels but does induce the accumulation of sufficient unesterified arachidonate by mass to achieve an increment in cellular levels of 38-75 microM. Little of this free arachidonate is released into the perifusion medium, and most remains associated with the islets. Glucose-induced hydrolysis of arachidonate from islet cell phospholipids is reflected by release of the arachidonate metabolite prostaglandin E2 (PGE2) from perifused islets. Both the depolarizing insulin secretagogue tolbutamide (which is thought to act by inducing closure of beta-cell ATP-sensitive K+ channels and the influx of extracellular Ca2+ through voltage-dependent channels) and the calcium ionophore A23187 have also been found to induce free arachidonate accumulation within and PGE2 release from islets. Surprisingly, a major fraction of glucose-induced eicosanoid release was found not to require Ca2+ influx and occurred even in Ca(2+)-free medium, in the presence of the Ca(2+)-chelating agent EGTA, and in the presence of the Ca2+ channel blockers verapamil and nifedipine. Exogenous arachidonic acid was found to amplify the insulin secretory response of perifused islets to submaximally depolarizing concentrations of KCl, and the maximally effective concentration of arachidonate was 30-40 microM. These observations suggest that glucose-induced phospholipid hydrolysis and free arachidonate accumulation in pancreatic islets are not simply epiphenomena associated with Ca2+ influx and that arachidonate accumulation may play a role in the signaling process which leads to insulin secretion.

Animals↗
PubMed1987

Cyclic AMP functions as a primary sexual signal in gametes of Chlamydomonas reinhardtii.

When Chlamydomonas reinhardtii gametes of opposite mating type are mixed together, they adhere by a flagella-mediated agglutination that triggers three rapid mating responses: flagellar tip activation, cell wall loss, and mating structure activation accompanied by actin polymerization. Here we show that a transient 10-fold elevation of intracellular cAMP levels is also triggered by sexual agglutination. We further show that gametes of a single mating type can be induced to undergo all three mating responses when presented with exogenous dibutyryl-cAMP (db-cAMP). These events are also induced by cyclic nucleotide phosphodiesterase inhibitors, which elevate endogenous cAMP levels and act synergistically with db-cAMP. Non-agglutinating mutants of opposite mating type will fuse efficiently in the presence of db-cAMP. No activation of mating events is induced by calcium plus ionophores, 8-bromo-cGMP, dibutyryl-cGMP, nigericin at alkaline pH, phorbol esters, or forskolin. H-8, an inhibitor of cyclic nucleotide-dependent protein kinase, inhibits mating events in agglutinating cells and antagonizes the effects of cAMP on non-agglutinating cells. Adenylate cyclase activity was detected in both the gamete cell body and flagella, with the highest specific activity displayed in flagellar membrane fractions. The flagellar membrane adenylate cyclase is preferentially stimulated by Mn++, unresponsive to NaF, GTP, GTP gamma S, AlF4-, and forskolin, and is inhibited by trifluoperazine. Cyclic nucleotide phosphodiesterase activity is also present in flagella. Our observations indicate that cAMP is a sufficient initial signal for all of the known mating reaction events in C. reinhardtii, and suggest that the flagellar cyclase and/or phosphodiesterase may be important loci of control for the agglutination-stimulated production of this signal.

Adenylyl Cyclases↗
PubMed1985

Role of microtubules in surfactant secretion.

In the isolated perfused rat lung and cultured type II cells, surfactant secretion and cellular adenosine 3',5'-cyclic monophosphate (cAMP) content was stimulated by beta-adrenergic agonists. Isoproterenol-induced surfactant secretion was inhibited by the antimicrotubule agents colchicine and vinblastine. Incorporation of [3H]glycerol into disaturated phosphatidylcholine was augmented by beta-adrenergic agents but was not significantly different from the enhanced incorporation rate when colchicine was present. This suggests that the augmented incorporation of [3H]glycerol into disaturated phosphatidylcholine was a secondary response to storage depletion rather than direct cAMP stimulation. beta-Adrenergic agents shifted the equilibrium in the isolated perfused rat lung and cultured type II cells to favor microtubules. The stimulatory effect of 1.0 microM isoproterenol on tubulin polymerization was observed as early as 1 min and was augmented 2.8-fold at a half-maximal stimulation of 4 nM in cultured type II cells. Cytochalasin B, an antimicrofilament agent, potentiated the isoproterenol-induced secretion. These results suggest that an intact microtubule-microfilament system may be obligatory for enhanced surfactant secretion and that beta-adrenergic agents not only induce surfactant release but also tubulin polymerization.

Animals↗
PubMed1979

CO2-induced kidney calcification.

Light microscopic examination of kidney tissue of guinea pigs exposed to 1.5% CO2, 21% O2, and balance N2 for periods as long as 42 days and of rats exposed to the same CO2 concentrations for up to 91 days showed that the incidence of focal kidney calcification increased with length of exposure. Calcification occurred primarily in the tubules of the renal cortex. Another group of guinea pigs were exposed to 1% CO2, 21% O2, and the balance N2 for periods up to six weeks and were later killed at regular intervals, together with control animals of the same litter. In the exposed animals, arterial PCO2 was elevated by 3-4 mmHg and hydrogen ions by about 4 nmol/liter. The standard bicarbonate level was lowered by 1-1.5 mmol, indicating a lack of renal reabsorption of bicarbonate (HCO3), which in turn placed greater stress on the bone buffer system and apparently caused bone calcium and phosphorus mobilization. Bone calcium and phosphorus levels exhibited a cyclic decrease, which resulted in cyclic hypercalcemia and hyperphosphatemia, after one week and six weeks of exposure to 1% CO2. Kidney calcium content increased significantly after two weeks of exposure (27%) and remained at this elevated level during subsequent exposures between the third and sixth weeks. These findings indicate that once the kidney calcification process has started, kidney mineralization is independent of fluctuations in the blood calcium level. A rise in plasma phosphate level that occurred after one day of exposure could have been a precipitating factor in the calcification process. The small but consistent increases in ionized calcium during a 4-week exposure to 1% CO2 may have stimulated the parathyroid, causing an increased blood calcium level that was independent of the two calcium tides in the blood associated with marked bone calcium loss.

Acid-Base Equilibrium↗
PubMed1979

Proliferation of pneumocyte II cells in prolonged exposure to 1% CO2.

Guinea pigs were exposed to 1% CO2 in a mixture of 21% O2, balance N2 and were killed at weekly intervals, together with control animals housed in the same type of environmental chamber and exposed to normal ambient CO2. The exposed animals showed a persistent elevation of PaCO2, averaging about 4 mmHg, and a small decrease in pH (-0.04 units). During the whole exposure period standard bicarbonate remained 1-1.5 mEq below control levels, indicating a failure of the kidney to increase bicarbonate reabsorption. Electron microscopic studies after 4 and 6 weeks of exposure to 1% CO2 showed ultrastructural changes of the lungs, consisting of marked increases in the size and number of pneumocyte II cells that were still present two weeks and to a lesser extent four weeks after recovery. Changes in the pneumocyte II cell were postulated to be compensatory reactions to impairing CO2 effects on the alveolar lining cell (Type I cell).

Animals↗