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Changes in intracellular Ca(2+) concentration ([Ca(2+)](i)) play a central role in neuronal differentiation. However, Ca(2+) signaling in this process remains poorly understood and it is unknown whether embryonic and adult stem cells share the same signaling pathways. To clarify this issue, neuronal differentiation was analyzed in two cell lines: embryonic P19 carcinoma stem cells (CSCs) and adult murine bone-marrow mesenchymal stem cells (MSC). We studied Ca(2+) release from the endoplasmic reticulum via intracellular ryanodine-sensitive (RyR) and IP(3)-sensitive (IP(3)R) receptors. We observed that caffeine, a RyR agonist, induced a [Ca(2+)](i) response that increased throughout neuronal differentiation. We also demonstrated a functional coupling between RyRs and L- but not with N-, P-, or Q-type Ca(v)1 Ca(2+) channels, both in embryonal CSC and adult MSC. We also found that agonists of L-type channels and of RyRs increase neurogenesis and neuronal differentiation, while antagonists of these channels have the opposite effect. Thus, our data demonstrate that in both cell lines RyRs control internal Ca(2+) release following voltage-dependent Ca(2+) entry via L-type Ca(2+) channels. This study shows that both in embryonal CSC and adult MSC [Ca(2+)](i) is controlled by a common pathway, indicating that coupling of L-type Ca(2+) channels and RyRs may be a conserved mechanism necessary for neuronal differentiation.

Spontaneous Ca(2+) events have been observed in diverse stem cell lines, including carcinoma and mesenchymal stem cells. Interestingly, during cell cycle progression, cells exhibit Ca(2+) transients during the G(1) to S transition, suggesting that these oscillations may play a role in cell cycle progression. We aimed to study the influence of promoting and blocking calcium oscillations in cell proliferation and cell cycle progression, both in neural progenitor and undifferentiated cells. We also identified which calcium stores are required for maintaining these oscillations. Both in neural progenitor and undifferentiated cells calcium oscillations were restricted to the G1/S transition, suggesting a role for these events in progression of the cell cycle. Maintenance of the oscillations required calcium influx only through inositol 1,4,5-triphosphate receptors (IP(3)Rs) and L-type channels in undifferentiated cells, while neural progenitor cells also utilized ryanodine-sensitive stores. Interestingly, promoting calcium oscillations through IP(3)R agonists increased both proliferation and levels of cell cycle regulators such as cyclins A and E. Conversely, blocking calcium events with IP(3)R antagonists had the opposite effect in both undifferentiated and neural progenitor cells. This suggests that calcium events created by IP(3)Rs may be involved in cell cycle progression and proliferation, possibly due to regulation of cyclin levels, both in undifferentiated cells and in neural progenitor cells.

The present study examined precipitate development induced in phosphate solutions by the ionophoric translocation of Ca2+ across a bulk organic solvent barrier. Experiments were conducted at pH 7.4 and 25 or 37 degrees in a three-compartment Pressman cell. The aqueous reaction (0, 2.2 or 22 mM phosphate, 100 mM K+) and donor (1.3 or 13 mM Ca2+, 0.8 mM Mg2+, 100 mM Na+) compartments were separated by a CHCl3 compartment rendered permeable to cations by the addition of the carboxylic ionophore X-537A (2 or 20 mM). The resultant cation movements increased Ca2+, Mg2+, and Na+ concentrations in the reaction compartment at the expense of K+ loss to the donor compartment. The magnitude of the K+ counterflow and the efficiency of the ionophore-mediated Ca2+ in equilibrium 2K+ exchange reaction resulted in appreciable Ca2+ overshoots in the reaction compartment. In the absence of phosphate, Ca2+ increases exceeded donor levels by several-fold. With phosphate present, the Ca2+ flux was sufficient to induced precipitation. Generally, the first solid formed was amorphous. The amorphous precipitate, however, was unstable and converted to an apatite-like crystalline phase. Both carbonate (26 mM) and Mg2+ (0.8 mM) in the reaction solution delayed but did not prevent the conversion. The possible relevance of these findings to matrix vesicle calcification is discussed.

Intra peritoneal administration of the short chain fatty acids, acetate, propionate and butyrate, in amounts calculated to reach 20 mM in total body water were given to fed and 48 hour starved male Wistar rats. One half hour after administration, the livers were freeze-clamped and the hepatic contents of various intermediary metabolites were measured. The liver content of total glycolytic intermediates was elevated by short chain fatty acids. In fed animals, the portion of glycolysis from fructose 1,6-bisphosphate (FBP) to PEP was elevated 2 to 4 fold. In 48 hour starved animals, where gluconeogenesis is active, the portion of the gluconeogenetic pathway from FBP to glucose was elevated 1.5 to 3.5 fold with the exception of the butyrate treated animals where blood glucose was not elevated. The metabolites of the hexose-monophosphate pathway that were measured, namely 6-phosphogluconate, ribulose 5-phosphate and xylose 5-phosphate were increased in both fed and starved animals. The free cytoplasmic [NAD+]/[NADH], [NADP+]/[NADPH], and [epsilon ATP]/[epsilon ADP] X [epsilon Pi] ratios were all decreased in both fed and starved animals after short chain fatty acid administration. The liver content of calcium increased 1.2 to 2 fold in fed animals and 2 to 3 fold in starved animals while total liver magnesium was either unchanged or increased only 1.2 times. The liver pyrophosphate (PPi) content increased a minimum of 10 fold in fed animals and over 100 fold in starved animals. In all cases no PPi could be detected in vivo by 31P NMR even though in the starved rats the PPi levels approached those of ATP. The liver content of inorganic Pi increased 1.3 to 1.5 fold in fed animals and 1.5 to 2 fold in starved animals. The total "rapidly metabolizing" Pi pool, that includes adenine and guanine nucleotides, glycolytic and shunt intermediates, Pi and PPi increased 1.3 times in fed animals (from 13.8 mumole/g fresh weight) and 1.5 to 1.7 fold in starved animals (from 15.7 mumol/g fresh weight). The total phosphate taken up from blood and entering the rapidly turning over pool of liver phosphate ranged between 4 and 12 mumols/g of liver.(ABSTRACT TRUNCATED AT 400 WORDS)

Dense bodies have been examined by electron microprobe techniques in air-dried whole mounts of dog, rabbit, and human platelets. On the basis of measurement of the intensities of the X-rays produced when dense bodies are probed for 100 seconds, dog and rabbit platelet dense bodies contain on the average less phosphorus and calcium, but more magnesium, than do human platelet dense bodies. Dense bodies of dog and rabbit platelets thus appear to resemble more closely those of pig platelets than those of human platelets.