Biomedical subjects

J Papassotiriou

Publications and source records attributed to J Papassotiriou.

3 recordsLinked to original sources

PubMed2001

Ca(2+)-activated Cl- channels in Ehrlich ascites tumor cells are distinct from mCLCA1, 2 and 3.

Using the whole-cell patch-clamp technique, we have studied the electrophysiological and pharmacological properties of the Ca(2+)-activated Cl- current present in Ehrlich cells. The currents activated slowly upon depolarization, deactivated upon hyperpolarization, and showed strong outward rectification. An increase in [Ca2+]i activated the current with an EC50 of 165.2 nM. Extracellular application of niflumic acid (100 microM) rapidly blocked the current in a voltage-dependent manner whereas sulfhydryl-modifying agents such as dithiothreitol (DTT, 1-2 mM) and N-ethylmaleimide (NEM, 100 microM) had no effect on Ca(2+)-activated currents in Ehrlich cells. Members of the recently discovered CLCA gene family are the only molecular candidates for Ca(2+)-activated Cl- channels cloned so far. Using RT-PCR we demonstrated that the appearance of a Ca(2+)-activated Cl- current in Ehrlich cells is not associated with the expression of the murine members of the CLCA family (mCLCA1-mCLCA3). Correspondingly, the kinetic and pharmacological properties of the Ca(2+)-activated current in Ehrlich cells differ from those of CLCA-associated currents, which are time independent and DTT sensitive. Thus, phenotypic differences in combination with RT-PCR data point to the existence of different molecular species for Ca(2+)-activated Cl- channels.

Animals↗

PubMed2000

Endothelial K(+) channel lacks the Ca(2+) sensitivity-regulating beta subunit.

Hyperpolarizing large-conductance, Ca(2+)-activated K(+) channels (BK) are important modulators of vascular smooth muscle and endothelial cell function. In vascular smooth muscle cells, BK are composed of pore-forming alpha subunits and modulatory beta subunits. However, expression, composition, and function of BK subunits in endothelium have not been studied so far. In patch-clamp experiments we identified BK (283 pS) in intact endothelium of porcine aortic tissue slices. The BK opener DHS-I (0.05-0.3 micromol/l), stimulating BK activity only in the presence of beta subunits, had no effect on BK in endothelium whereas the alpha subunit selective BK opener NS1619 (20 micromol/l) markedly increased channel activity. Correspondingly, mRNA expression of the beta subunit was undetectable in endothelium, whereas alpha subunit expression was demonstrated. To investigate the functional role of beta subunits, we transfected the beta subunit into a human endothelial cell line (EA.hy 926). beta subunit expression resulted in an increased Ca(2+) sensitivity of BK activity: the potential of half-maximal activation (V(1/2)) shifted from 73.4 mV to 49.6 mV at 1 micromol/l [Ca(2+)](i) and an decrease of the EC(50) value for [Ca(2+)](i) by 1 microM at +60 mV was observed. This study demonstrates that BK channels in endothelium are composed of alpha subunits without association to beta subunits. The lack of the beta subunit indicates a substantially different channel regulation in endothelial cells compared to vascular smooth muscle cells.

Animals↗

PubMed1993

Flow-cytometric analysis of reticulocytes in normal cord blood.

We performed precise reticulocyte counts and a reticulocyte maturation study according to ribosomal RNA (rRNA) content, in normal cord blood. For this purpose we analyzed 35 cord blood specimens corresponding to a mean gestational age of 39.2 weeks (range 38-41). In all specimens complete blood counts were performed with the H*1 (Technicon, Bayer) analyzer. Reticulocyte maturation study and counts were conducted by the R-1000 (Sysmex) reticulocyte analyzer. We obtained the following measurements (mean +/- 1 SD): reticulocyte percentage 3.11 +/- 0.75% and reticulocyte absolute count 137.3 +/- 33.3 x 10(9)/l. There was no correlation between the reticulocyte counts and the duration of gestation or the type of labor (normal, forceps assisted or cesarean section). Reticulocyte subpopulations with different rRNA content and maturation were expressed as reticulocytes with high (HFR), median (MFR) and low (LFR) fluorescence of the fluorochrome auramine bound to rRNA. Normal cord values were: HFR% = 13.6 +/- 2.4, MFR% = 22.5 +/- 2.4 and LFR% = 63.9 +/- 4.3. Reference maturation subpopulations were assessed for comparison in 180 samples of healthy adults (90 males and 90 females) and were found HFR% = 1.0 +/- 0.8, MFR% = 9.7 +/- 3.3 and LFR% = 89.2 +/- 3.4. The HFR% and MFR% were significantly higher while LFR% was significantly lower (p < 0.001) in cord compared to adult blood, denoting a shift to more immature reticulocyte forms. The above values are provided as normal reference data of the reticulocyte maturation profile in full-term cord blood.

Adult↗