Biomedical subjects

G Hofmeier

Publications and source records attributed to G Hofmeier.

At least 19 recordsLinked to original sources

PubMed2001

A new method for histological microdissection utilizing an ultrasonically oscillating needle: demonstrated by differential mRNA expression in human lung carcinoma tissue.

Molecular analysis of microdissected tissue samples is used for analyzing tissue heterogeneity of histological specimens. We have developed a rapid one-step microdissection technique, which was applied for the selective procurement of tissue areas down to a minimum of 10 cell profiles. The special features of our microdissection system consist of an ultrasonically oscillating needle and a piezo-driven micropipette. The validity of this technique is demonstrated in human lung large-cell carcinoma by real-time quantitative reverse transcriptase-polymerase chain reaction assays of vimentin, cyclin D1, and carcinoembryonic antigen after linear RNA amplification. mRNA expression values of microdissected samples scattered around those of bulk tumor tissue and showed differential mRNA expression between samples of tumor parenchyma and supportive stromal cells for vimentin and carcinoembryonic antigen as confirmed by immunohistochemistry. In conclusion, this procedure requires simple equipment, is easily performed, and delivers microdissected tissue samples of oligocellular clusters suitable for further molecular analysis.

Carcinoembryonic Antigen↗

PubMed1983

Stimulation of a sodium influx by cAMP in Helix neurons.

Brief pressure injections of aqueous solutions of cAMP in identified neurons of Helix pomatia caused depolarizations which lasted for tens of seconds. In voltage-clamped neurons an inward current of similar duration was induced which saturated at 10 microA/cm2 cell surface. In the range of negative membrane potentials with little voltage-dependent activation, this current was not accompanied by a change in membrane conductance. The inward current was not produced by injection of ATP, ADP, adenosine, inosine or cGMP. cAMP derivatives produced longer-lasting effects. Prolongation of the inward current was also observed after inhibition of the phosphodiesterase by IBMX. Drugs which block active transport had no effect on the response to cAMP injection. The inward current depended on extracellular sodium, and was maximal when all other mono- and divalent cations were replaced by Na+. The cAMP-induced current was accompanied by a transient increase in [Na+]i, but there was no change in [Cl-]i. Li+ could largely substitute for Na+; Ca2+ was less effective. Addition of Mg2+ or Ca2+ to solutions containing a high Na+-concentration inhibited the response. Internal acidification with HCl reversibly enhanced the inward current. These data indicate that the depolarizing effect of cAMP can be accounted for by an inward movement of Na-ions, and that the effect is augmented by H+-ions.

1-Methyl-3-isobutylxanthine↗

PubMed1982

Stimulus-induced changes in extracellular Na+ and Cl- concentration in relation to changes in the size of the extracellular space.

Extracellular Na+ - and Cl- -concentrations ([Na+]o, [Cl-]o) were recorded with ion-selective microelectrodes during repetitive stimulation and stimulus-induced self-sustained neuronal afterdischarges (SAD) in the sensorimotor cortex of cats. In all cortical layers [Na+]o initially decreased by 4-7 mM. In depths of more than 600 micrometer below the cortical surface such decreases usually turned into increases of 2-6 mM during the course of the SADs, whereas in superficial layers [Na+]o never rose above its resting level. [Cl-]o always showed an increase in the course of the SADs often preceded by an initial small decrease. The average increase at a depth of 1,000 micrometers was about 7 mM. [Cl-]o reached peak values at about the end of the ictal period, whereas [Na+]o reached its maximum shortly after the end of the SAD, at times when [K+]o was still elevated above the baseline concentration. These data indicate that the extracellular osmolarity can increase during SAD by up to 30 mM. Such an increase in osmolarity can be explained by an increase in the number of intracellular particles, caused by cleavage of larger molecules during enhanced metabolism. This could lead to cell-swelling due to passive water influx from the extracellular space (ES). However, the resulting reduction of the size of the ES is calculated to be less than 10% for an increase in intracellular osmolarity by 30 mOsm. This value is too small as compared to previously measured ES-reductions under similar conditions (i.e., 30% reduction at 1,000 micrometers; Dietzel et al. 1980). Reductions of the size of the ES that accompany the observed changes in the ionic environment, are quantitatively explained on the basis of the extended glial buffering mechanism described in the preceding paper.

Animals↗

PubMed1982

Properties of a calcium- and voltage-activated potassium current in Helix pomatia neurons.

A calcium- and voltage-dependent current was found to be the principal outward current in identified Helix neurons. The current depends on the presence of [Ca2+]0, with half maximal activation at 1 mM [Ca2+]0, and it saturates beyond about 5 mM. The current is termed IK(Ca) since the charge carried by it corresponds to the amount of potassium ions transferred from the cell interior, as determined from the increase in K+ concentration in the external volume with K+ liquid ion-exchanger microelectrodes. IK(Ca) is characterized by cell shaped isochronal I/V curves. The peaks of these curves move from +30 mV to about +70 mV with an increase of the time of measurement from 30-200 ms. IK(Ca) rise times have a minimum of 10-15 ms at low depolarization around 0 mV, but increase about exponentially with more positive potentials. A tenfold decrease in [Ca2+]0 over the range of 30 to 0.3 mM also produces an increase in rise time, equivalent to a positive shift of potential by 20 mV. On repolarization of the membrane IK(Ca) disappears much faster than the intracellularly accumulated Ca2+, with a time constant which is similar to the minimum activation time constant.

Animals↗

PubMed1982

Activation characteristics of the calcium-dependent outward potassium current in Helix.

The activation of calcium-dependent outward potassium current [IK(Ca)] by shortlasting Ca2+ inward currents was studied. These Ca2+ currents were produced either by small depolarizing pulses preceding the larger depolarizations or by interposed repolarizations (I.R.s) starting from depolarized membrane potentials. IK(Ca) then develops with a potential-invariant time course (half time 6-12 ms) and the normally bell-shaped isochronal IK(Ca)/V curve, measured at between 30 and 300 ms, is straightened. However, there Ca2+ - injecting pulses, of any amplitude and duration, do not increase the steady-state conductance to values beyond those measured with single step depolarizations to lower potentials. varied in length, activation of IK(Ca) increased linearly with the during depolarization to near the supposed calcium equilibrium potential with no further Ca2+ influx. When I.R.s are varied in length, activation of I(Ca) increases linearly with the amount of Ca2+ current. Fading of activation during I.R. follows a time course nearly ten times slower than activation and is not expressed in tail currents. The time course of IK(Ca) is described by a function defined only by voltage parameters of activation combined with a minimum activation time constant which is similar to that found in tail currents. Peak location and general form of the IK(Ca)/V relationship for times up to several hundred milliseconds are well predicted without the necessity of explicitly account for actual calcium entry.

Animals↗

PubMed1981

The time courses of intracellular free calcium and related electrical effects after injection of CaCl2 into neurons of the snail, Helix pomatia.

Controlled quantities of 100 mM aqueous CaCl2 solutions were pressure injected into voltage-clamped neurons with a resolution of 10(-11) 1. Ca2+-selective microelectrodes monitored the time course of changes in [Ca2+]i. At a membrane potential of -50 mV CaCl2 quantities in the range of 1% of the cell volume induced an inward current, associated with a conductance increase and having an equilibrium potential between -20 and +20 mV, which accompanied the rise in [Ca2+]i. An artifactual origin of the inward current by the injection procedure or by calcium screening of membrane sites could be excluded. The calcium-induced hyperpolarizing conductance, producing an outward current at -50 mV, followed the inward current and reached maximum during the late decline in [Ca2+]i. In most cases its development was separated from the inward current by an intermediate relative decrease of the membrane conductance. Neither of the two transient conductance increases showed a particular dependence on voltage. Renewed Ca2+ injection quickly decreased the calcium-induced hyperpolarizing conductance for several seconds. Ca2+ injections below 0.05% of the cell volume mostly produced pure outward currents or hyperpolarizing responses. Partial substitution of extracellular CaCl2 by NiCl2 decreased the hyperpolarizing response but not the initial inward current. The immediate effects of increased [Ca2+]i are activation of a depolarizing conductance and the partial block of the late hyperpolarizing conductance. The latter is probably produced through intermediate steps after increasing [Ca2+]i.

Animals↗

PubMed1980

Transient changes in the size of the extracellular space in the sensorimotor cortex of cats in relation to stimulus-induced changes in potassium concentration.

The time course of local changes of the extracellular space (ES) was investigated by measuring concentration changes of repeatedly injected tetramethylammonium (TMA+) and choline (Ch+) ions for which cell membranes are largely impermeable. After stimulus-induced extracellular [K+] elevations the delta [TMA+] and delta [Ch+] signals recorded with nominally K+-selective liquid ion-exchanger microelectrodes increased by up to 100%, thus indicating a reduction of the ES down to one half of its initial size. The shrinkage was maximal at sites where the K+ release into the ES was also largest. At very superficial and deep layers, however, considerable increases in extracellular K+ concentration were not accompanied by significant reductions in the ES. These findings can be explained as a consequence of K+ movement through spatially extended cell structures. Calculations based on a model combining the spatial buffer mechanism of Kuffler and Nicholls (1966) to osmolarity changes caused by selective K+ transport through primarily K+ permeable membranes support this concept. Following stimulation additional iontophoretically induced [K+]0 rises were reduced in amplitude by up to 35%, even at sites where maximal decreases of the ES were observed. This emphasizes the importance of active uptake for K+ clearance out of the ES.

Animals↗

PubMed1979