Key points
T‐type Ca2+ channels are expressed in the ventricular myocytes of the fetal and perinatal heart, but are downregulated as development progresses. However, these channels are re‐expressed ...in adult cardiomyocytes under pathological conditions.
Hypoxia induces the upregulation of the T‐type Ca2+ channel Cav3.2 mRNA in cardiac myocytes, whereas Cav3.1 mRNA is not significantly altered.
The effect of hypoxia on Cav3.2 mRNA requires hypoxia inducible factor‐1α (HIF‐1α) stabilization and involves the small monomeric G‐protein RhoA and its effector ROCKI.
Our results suggest that the hypoxic regulation of the Cav3.2 channels may be involved in the increased probability of developing arrhythmias observed in ischemic situations, and in the pathogenesis of diseases associated with hypoxic Ca2+ overload.
T‐type Ca2+ channels are expressed in the ventricular myocytes of the fetal and perinatal heart, but are normally downregulated as development progresses. Interestingly, however, these channels are re‐expressed in adult cardiomyocytes under pathological conditions. We investigated low voltage‐activated T‐type Ca2+ channel regulation in hypoxia in rat cardiomyocytes. Molecular studies revealed that hypoxia induces the upregulation of Cav3.2 mRNA, whereas Cav3.1 mRNA is not significantly altered. The effect of hypoxia on Cav3.2 mRNA was time‐ and dose‐dependent, and required hypoxia inducible factor‐1α (HIF‐1α) stabilization. Patch‐clamp recordings confirmed that T‐type Ca2+ channel currents were upregulated in hypoxic conditions, and the addition of 50 μm NiCl2 (a T‐type channel blocker) demonstrated that the Cav3.2 channel is responsible for this upregulation. This increase in current density was not accompanied by significant changes in the Cav3.2 channel electrophysiological properties. The small monomeric G‐protein RhoA and its effector Rho‐associated kinase I (ROCKI), which are known to play important roles in cardiovascular physiology, were also upregulated in neonatal rat ventricular myocytes subjected to hypoxia. Pharmacological experiments indicated that both proteins were involved in the observed upregulation of the Cav3.2 channel and the stabilization of HIF‐1α that occurred in response to hypoxia. These results suggest a possible role for Cav3.2 channels in the increased probability of developing arrhythmias observed in ischaemic situations, and in the pathogenesis of diseases associated with hypoxic Ca2+ overload.
Key points
T‐type Ca
2+
channels are expressed in the ventricular myocytes of the fetal and perinatal heart, but are downregulated as development progresses. However, these channels are re‐expressed ...in adult cardiomyocytes under pathological conditions.
Hypoxia induces the upregulation of the T‐type Ca
2+
channel Ca
v
3.2 mRNA in cardiac myocytes, whereas Ca
v
3.1 mRNA is not significantly altered.
The effect of hypoxia on Ca
v
3.2 mRNA requires hypoxia inducible factor‐1α (HIF‐1α) stabilization and involves the small monomeric G‐protein RhoA and its effector ROCKI.
Our results suggest that the hypoxic regulation of the Ca
v
3.2 channels may be involved in the increased probability of developing arrhythmias observed in ischemic situations, and in the pathogenesis of diseases associated with hypoxic Ca
2+
overload.
Abstract
T‐type Ca
2+
channels are expressed in the ventricular myocytes of the fetal and perinatal heart, but are normally downregulated as development progresses. Interestingly, however, these channels are re‐expressed in adult cardiomyocytes under pathological conditions. We investigated low voltage‐activated T‐type Ca
2+
channel regulation in hypoxia in rat cardiomyocytes. Molecular studies revealed that hypoxia induces the upregulation of Ca
v
3.2 mRNA, whereas Ca
v
3.1 mRNA is not significantly altered. The effect of hypoxia on Ca
v
3.2 mRNA was time‐ and dose‐dependent, and required hypoxia inducible factor‐1α (HIF‐1α) stabilization. Patch‐clamp recordings confirmed that T‐type Ca
2+
channel currents were upregulated in hypoxic conditions, and the addition of 50 μ
m
NiCl
2
(a T‐type channel blocker) demonstrated that the Ca
v
3.2 channel is responsible for this upregulation. This increase in current density was not accompanied by significant changes in the Ca
v
3.2 channel electrophysiological properties. The small monomeric G‐protein RhoA and its effector Rho‐associated kinase I (ROCKI), which are known to play important roles in cardiovascular physiology, were also upregulated in neonatal rat ventricular myocytes subjected to hypoxia. Pharmacological experiments indicated that both proteins were involved in the observed upregulation of the Ca
v
3.2 channel and the stabilization of HIF‐1α that occurred in response to hypoxia. These results suggest a possible role for Ca
v
3.2 channels in the increased probability of developing arrhythmias observed in ischaemic situations, and in the pathogenesis of diseases associated with hypoxic Ca
2+
overload.
Voltage-dependent K(+) channel gating is influenced by the permeating ions. Extracellular K(+) determines the occupation of sites in the channels where the cation interferes with the motion of the ...gates. When external K(+) decreases, some K(+) channels open too briefly to allow the conduction of measurable current. Given that extracellular K(+) is normally low, we have studied if negatively charged amino acids in the extracellular loops of Shaker K(+) channels contribute to increase the local K(+). Surprisingly, neutralization of the charge of most acidic residues has minor effects on gating. However, a glutamate residue (E418) located at the external end of the membrane spanning segment S5 is absolutely required for keeping channels active at the normal external K(+). E418 is conserved in all families of voltage-dependent K(+) channels. Although the channel mutant E418Q has kinetic properties resembling those produced by removal of K(+) from the pore, it seems that E418 is not simply concentrating cations near the channel mouth, but has a direct and critical role in gating. Our data suggest that E418 contributes to stabilize the S4 voltage sensor in the depolarized position, thus permitting maintenance of the channel open conformation.
We have described a new population of adult neural stem cells residing in the carotid body, a chemoreceptor organ in the peripheral nervous system. These progenitor cells support neurogenesis in vivo ...in response to physiological stimuli like hypoxemia, and give rise to multipotent neurospheres in culture. Studying the biology of CB stem cells helps to understand the physiological adaptations of the organ, and might shed light on the pathogenesis of CB tumors. Understanding proliferation and differentiation of these cells will enable their use for cell therapy against neurodegenerative diseases.
We have studied the effects of mutations of amino acids in the pore (positions 447 and 449) and the elevation of extracellular
K + on the closing and opening kinetics of Shaker B K + channels ...transiently expressed in Chinese hamster ovary (CHO) cells.
Mutant D447E had closing and C-type inactivation kinetics which were faster than the wild-type channel. These processes were
slowed by increasing extracellular K + and in these conditions the channels exhibited linear instantaneous current-voltage relationships. Thus, the mutation seems
to produce uniform decrease of occupancy by K + in sites along the channel pore where the cation competes with closing and C-type inactivation.
In other mutants also showing K + -dependent fast C-type inactivation, closing was found to be slower than in the wild-type channel and insensitive to variations
in external K + . These characteristics were particularly apparent in mutant T449K which even in high K + has a non-linear instantaneous current-voltage relationship with marked saturation of the inward current recorded at negative
membrane potentials. Hence, in this channel type occupation by K + of the pore appears to be non-uniform with low occupancy of sites near the outer entrance and saturation of the sites accessible
from the internal solution.
The results show that channel closing is influenced by changes in the pore structure leading to alterations in the occupation
of the channels by permeant cations. The differential effects of pore mutations and high external K + on closing and C-type inactivation indicate that the respective gates are associated with separate domains of the molecule.
Point mutations in the pore sequence can also lead to modifications in channel opening. In general, channels with fast C-type
inactivation also show a fast rising phase of activation. However, these effects appear not to be due to primary modifications
of the activation process but to arise from the coupling of activation and C-type inactivation.
These data, demonstrating that the pore structure influences most of the gating parameters of K + channels, give further insight into the mechanisms underlying the modulation of K + channel function by changes in the ionic composition in the extracellular milieu.
A, anti-proCOL11A1 mAb, positive control (inset): cell line A204; B, desmin, positive control (inset): appendix; C, alpha-Smooth Muscle Actin, positive control (inset): appendix; D, vimentin, ...positive control (inset) : appendix) ; E, GFAP, positive control (inset) : astrocytoma). A, anti-proCOL11A1 mAb , positive control (inset): cell line A204); B, desmin, positive control (inset): appendix); C, alpha-Smooth Muscle Actin , positive control (inset) : appendix) ; D, vimentin , positive control (inset): appendix) ; E, GFAP, positive control (inset) : astrocytoma). (2013) Correction: Overexpression of COL11A1 by Cancer-Associated Fibroblasts: Clinical Relevance of a Stromal Marker in Pancreatic Cancer.
Abstract Renoportal anastomosis has been used as the primary portal revascularization technique in grade 4 portal thrombosis, but never after posttransplant portal thrombosis. A cirrhotic patient ...with hepatocellular carcinoma and partial portal thrombosis of two-thirds of the lumen was transplanted. The thrombus was removed and good portal flow obtained upon reperfusion (2.8 L/min). On the ninth postoperative day Doppler ultrasound revealed complete portal thrombosis extending from the splenomesenteric confluence. At emergency reoperation, we removed the newly formed thrombus. Portal vein branches were flushed with heparin and urokinase. After reconstruction of the anastomosis, we achieved a flow of 1.1 L/min. Rethrombosis occurred again on day 13. At reoperation, thrombus was removed again. However, this time portal flow was not recovered, due to hepatofugal flow associated with both the presence of collaterals and pancreatic edema. A left renoportal anastomosis was performed using an interposed iliac vein graft. A catheter was placed into the portal vein through a recanalization of the umbilical vein of the graft. After urokinase perfusion, portal inflow was 1.7 L/min. The postoperative course was satisfactory, with progressive normalization of liver tests and no further thrombosis. Persistent ascites improved with treatment. Angiography on day 41 showed good portal flow from the renal vein, with uniform distribution within the liver. A renoportal anastomosis can be useful for recovery of liver failure after posttransplant portal thrombosis, in the absence of portal flow.
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