We report here the expression and properties of the
intermediate-conductance Ca2+-activated K+ (IKCa)
channel in the GL-15 human glioblastoma cell line.
Macroscopic IKCa currents on GL-15 cells displayed
a mean amplitude of 7.2±0.8 pA/pF at 0 mV, at day 1
after plating. The current was inhibited by clotrimazole
(CTL, IC50=257 nM), TRAM-34 (IC50=55 nM), and
charybdotoxin (CTX, IC50=10.3 nM). RT-PCR analysis
demonstrated the expression of mRNA encoding
the IKCa channel in GL-15 cells. Unitary currents recorded
using the inside-out configuration had a conductance
of 25 pS, a KD for Ca2+ of 188 nM at -100
mV, and no voltage dependence. We tested whether
the IKCa channel expression in GL-15 cells could be
the result of an increased ERK activity. Inhibition of
the ERK pathway with the MEK antagonist PD98059
(25 µM, for 5 days) virtually suppressed the IKCa current
in GL-15 cells. PD98059 treatment also increased
the length of cellular processes and up-regulated the
astrocytic differentiative marker GFAP. A significant
reduction of the IKCa current amplitude was also observed
with time in culture, with mean currents of
7.17±0.75 pA/pF at 1-2 days, and 3.11±1.35 pA/pF
at 5-6 days after plating. This time-dependent downregulation
of the IKCa current was not accompanied
by changes in the ERK activity, as assessed by
immunoblot analysis. Semiquantitative RT-PCR analysis
demonstrated a ~35% reduction of the IKCa channel
mRNA resulting from ERK inhibition and a ~50%
reduction with time in culture.
It has been demonstrated that in hepatocyte nuclei the chromatin phospholipid fraction is localized near the RNA in decondensed chromatin. The aim of the present study was to see if there is any linkage between phospholipids and other nuclear components. Isolated hepatocyte nuclei and nuclear membranes were treated with deoxyribonuclease and ribonuclease. No loss of phospholipids was observed after DNA digestion, whereas 48% was lost following enzymatic RNA removal. This loss of phospholipids, localized either near the membrane or inside the nucleus, was not homogeneous for all phospholipids: phosphatidylserine and sphingomyelin being the most affected. It can be concluded that 48% of nuclear phospholipids, in particular sphingomyelin, is lost with RNA removal. This result is discussed in view of a possible role of phospholipids in DNA synthesis and RNA transcription.
model innovation, Diversity, Inter-organizational networks, ProactivenessThe relevance of business model innovation (BMI) for strategic renewal and competitive advantage has been increasingly recognized by both strategy scholars and managers. In this paper, we explore how inter-organizational networks and firms' proactiveness influence BMI. By examining Dutch design companies, we show that having a network of companies with different sizes has a positive effect on BMI. We also observe a positive effect of ties change. Finally, we show the importance of firms' proactiveness. Through the discussion of network elements and proactiveness as antecedents of BMI, we contribute to the business model and social network literature.
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