When is high-Ca+ microdomain required for mitochondrial Ca+ uptake?

Ca(2+) release from IP(3)-sensitive stores in the endoplasmic reticulum (ER) induced by Ca(2+)-mobilizing agonists generates high-Ca(2+) microdomains between ER vesicles and neighbouring mitochondria. Here we present a model that describes when such microdomains are required and when submicromolar [Ca(2+)] is sufficient for mitochondrial Ca(2+) uptake. Mitochondrial Ca(2+) uptake rate in angiotensin II-stimulated H295R adrenocortical cells correlates with the proximity between ER vesicles and the mitochondrion, reflecting the uptake promoting effect of high-Ca(2+) peri-mitochondrial microdomains. Silencing or inhibition of p38 mitogen-activated protein kinase (MAPK) or inhibition of the novel isoforms of protein kinase C enhances mitochondrial Ca(2+) uptake and abolishes the positive correlation between Ca(2+) uptake and ER-mitochondrion proximity. Inhibition of protein phosphatases attenuates mitochondrial Ca(2+) uptake and also abolishes its positive correlation with ER-mitochondrion proximity. We postulate that during IP(3)-induced Ca(2+) release, Ca(2+) uptake is confined to ER-close mitochondria, because of the simultaneous activation of the protein kinases. Attenuation of Ca(2+) uptake prevents Ca(2+) overload of mitochondria and thus protects the cell against apoptosis. On the other hand, all the mitochondria accumulate Ca(2+) at a non-inhibited rate during physiological Ca(2+) influx through the plasma membrane. Membrane potential is higher in ER-distant mitochondria, providing a bigger driving force for Ca(2+) uptake. Our model explains why comparable mitochondrial Ca(2+) signals are formed in response to K(+) and angiotensin II (equipotent in respect to global cytosolic Ca(2+) signals), although only the latter generates high-Ca(2+) microdomains.

Role of gamma-aminobutyric acid in early neuronal development: studies with an embryonic neuroectodermal stem cell clone.

gamma-Aminobutyric acid (GABA) has been known to function as an autocrine/paracrine signal molecule in addition to its well-known inhibitory neurotransmitter function. Studies on the developing brain and on primary brain cell cultures provided evidence for a variety of GABA functions in periods preceding the formation of synapses. The exact role of GABA in the early neural development, however, is still not well understood. In this study, one-cell-derived NE-4C neuroectodermal stem cells were induced to form neurons and astrocytes in vitro, and the role of GABA was investigated in defined phases of neurogenesis. Noninduced NE-4C cells contained GABA, expressed GABA(A)R alpha subunits, and carried functional GABA(A) ion channels. A moderate cytoplasmic GABA content was detected during the entire period of differentiation. By the time of the formation of differentiated neurons, neuron-like cells with both high and low GABA content were clearly distinguishable. HPLC analysis indicated that NE-4C cells released GABA into their fluid environment during all stages of neuronal development. By using the patch-clamp technique, GABA-evoked currents were recorded during the entire proliferation/differentiation period, whereas a GABA-evoked increase in intracellular Ca(2+) was detected only during the maturation of postmitotic neuronal precursors. Bicuculline blocked both the ion currents and the [Ca(2+)](i) increase in response to GABA. Neuron formation was facilitated by GABA through GABA(A) ion channels during postmitotic differentiation, but not earlier during the phases of cell fate commitment. Although the data clearly demonstrate an early responsiveness to GABA, understanding the significance of GABA influence in early neural cell fate decisions will require further investigation.

Intravenous excretory urography using Optiray in office urology.

Experiences with the nonionic contrast medium Optiray 300 were analyzed in 120 consecutive patients who underwent intravenous urography. Allergic diathesis was recorded prior to the examination in 12.5% of the patients, pretreatment was given in only 3 cases. The clinical safety of Optiray was outstanding, no adverse reactions were noted. Diagnostic quality of the radiographs was excellent in 78% and good in 22% of the cases. Optiray is considered to be a safe and effective contrast agent for use in intravenous excretory urography.

Electronic bladder stimulation in spinal cord paralysis.

Authors performed electronic stimulation of the paralysed bladder that was attributed to various innervation troubles. For this purpose, they implanted 10 patients with stimulator Model PMS-3, each with 8 electrodes. In three cases, outside factors (like endocarditis, pyelonephritis aposthematosa, and progress of paralysis in the limbs) forced them to remove the stimulator. The other cases can be declared as successful, for complete bladder emptying has been obtained. The authors want to emphasize that patients with an implanted stimulator can dispense with an indwelling catheter thereby avoiding vesicoureteral reflux. The absence of recurrent pyelonephritis results in prolonged health. This new technique seems to be appropriate, especially in peripheric paralysis, while central paralysis connected with fibrosis of the bladder neck often requires additional surgical intervention, e.g. transurethral resection.