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Biomedical subjects

L Izu

Publications and source records attributed to L Izu.

4 recordsLinked to original sources
PubMed1998

Ca2+ sparks triggered by patch depolarization in rat heart cells.

The goal of this study was to examine the relationship between Ca2+ entry through L-type Ca2+ channels and local [Ca2+]i transients (Ca2+ sparks) in single rat cardiac ventricular cells. L-type Ca2+ channels were activated by depolarization of cell-attached membrane patches, and [Ca2+]i was measured simultaneously as fluo 3 fluorescence using laser scanning confocal microscopy. Patch depolarization with Ca2+ as the charge carrier (10 or 110 mmol.L(-1)) significantly increased the probability of the occurrence of Ca2+ sparks (Ca2+ spark rate) only in the volume of cytoplasm located immediately beneath the membrane patch (basal Ca2+ spark rate, 119 Ca2+ sparks.cell(-1).s(-1); patch depolarization Ca2+ spark rate, 610 Ca2+ sparks.cell(-1).s(-1); P<.005). With Ba2+ in the pipette solution (10 mmol.L(-1)), patch depolarization was not associated with an increased Ca2+ spark rate at the position of the pipette or at any other sites distant from the pipette. Therefore, Ca2+ entry and not voltage per se was a necessary event for the occurrence of Ca2+ sparks. Under identical experimental conditions, patch depolarization experiments opened single L-type Ca2+ channels with a single-channel conductance of 19 pS with Ba2+ as the charge carrier. Although single-channel openings could not be resolved when Ca2+ was the charge carrier, ensemble averages yielded an inward current of up to 0.75 pA. The results suggest that voltage-activated Ca2+ entry through one or a small number of L type Ca2+ channels triggers the release of Ca2+ only from the sarcoplasmic reticulum in direct proximity to those L-type Ca2+ channels. The relatively low probability of triggering Ca2+ sparks may have resulted from some alteration of excitation-contraction coupling associated with the technique of the cell-attached patch clamp.

Animals↗
PubMed1998

Downregulation of a human colonic sialyltransferase by a secondary bile acid and a phorbol ester.

Fecal constituents such as bile acids and increased sialylation of membrane glycoproteins by alpha-2,6-sialyltransferase (HST6N-1) may contribute to colorectal tumorigenesis. We hypothesized that bile acids and phorbol ester [12-O-tetradecanoylphorbol-13-acetate (TPA)] would upregulate HST6N-1 in colonic cells. However, deoxycholate (DOC) (300 mumol/l), a secondary bile acid, and TPA (20 ng/ml) decreased expression of an approximately 100-kDa glycoprotein bearing alpha-2,6-linked sialic acid in a colon cancer cell line (T84) in vitro. HST6N-1 mRNA levels were reduced approximately 80% by treatment (< or = 24 h) with DOC or TPA but not by cholate, a primary bile acid. Treatment (24 h) with DOC or TPA decreased activity of this enzyme to 30% and 13% of control, respectively. These effects of DOC and TPA were transcriptional and were mediated by Ca2+ and protein kinase C, respectively. Thus DOC and TPA both downregulated, and did not upregulate, alpha-2,6-sialyltransferase expression in vitro, but by different transduction pathways. As colorectal tumors grow, their progressive removal from the fecal milieu that normally downregulates this enzyme may favor invasion and metastasis.

Calcium↗
PubMed1997

G proteins activate ionic conductances at multiple sites in T84 cells.

We examined the role of G proteins in activation of ionic conductances in isolated T84 cells during cholinergic stimulation. When cells were whole cell voltage clamped to the K+ equilibrium potential (E(K)) or Cl- equilibrium potential (E(Cl)) under standard conditions, the cholinergic agonist, carbachol, induced a large oscillating K+ current but only a small inward current. Addition of the GDP analogue, guanosine 5'-O-(2-thiodiphosphate), to pipettes blocked the ability of carbachol to activate the K+ current. Addition of the nonhydrolyzable GTP analogue, guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS), to pipettes stimulated large oscillating K+ and inward currents. This occurred even when Ca2+ was absent from the bath but not when the Ca2+ chelator, ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, was added to pipettes. When all pipette and bath K+ was replaced with Na+ and cells were voltage clamped between E(Na) and E(Cl), GTPgammaS activated oscillating Na+ and Cl- currents. Finally, addition of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] to pipettes activated large oscillating K+ currents but only small inward currents. These results suggest that a carbachol-induced release of Ca2+ from intracellular stores is activated by a G protein through the phospholipase C-Ins(1,4,5)P3 signaling pathway. In addition, this or another G protein activates Cl- current by directly gating Cl- channels to increase their sensitivity to Ca2+.

Calcium↗