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Biomedical subjects

F Lang

Publications and source records attributed to F Lang.

At least 397 records · Page 22Linked to original sources
PubMed1988

Enhancement of intracellular calcium concentration by extracellular ATP and UTP in Madin Darby Canine Kidney cells.

Fura2 - fluorescence was utilized to test for the effect of extracellular nucleotides on intracellular calcium concentration of subconfluent Madin-Darby Canine Kidney (MDCK)-cells. Extracellular ATP (10 mumol/l) and UTP (10 mumol/l) lead to rapid (within seconds), sustained, and fully reversible enhancement of intracellular calcium concentration from 138 +/- 9 nmol/l (n = 27), to 1561 +/- 260 nmol/l (n = 10) and 3435 +/- 949 nmol/l (n = 5), respectively. Half maximal effects are observed at some 1 mumol/l. In the absence of extracellular calcium the effect of ATP is transient, pointing to release of intracellular calcium. The sustained effect in the presence of extracellular calcium indicates that the nucleotides in addition recruit calcium from extracellular space.

Adenosine Triphosphate↗
PubMed1988

Effects of extracellular nucleotides on electrical properties of subconfluent Madin Darby canine kidney cells.

ATP and ADP but not AMP lead to sustained hyperpolarization of Madin Darby canine kidney (MDCK) cells. The present study has been performed to test for an influence of other nucleotides on the potential difference across the cell membrane (PD) in subconfluent MDCK cells. PD has been continuously monitored with conventional microelectrodes during rapid exchange of extracellular fluid. Application of 1 mumol/1 UTP leads to a rapid (less than 2 s) hyperpolarization of the cell membrane by -17.0 +/- 0.4 mV (from -50.1 +/- 0.6 mV), a reduction of cell membrane resistance and an increase of the sensitivity of PD to alterations of extracellular potassium. The concentration needed for half maximal effect of UTP is approximately equal to 0.2 mumol/1. ITP is similarly effective, whereas UDP, GTP and GDP are less effective. Up to 1 mmol/1 UMP, GMP, TTP or CTP do not significantly alter PD. In calcium-free extracellular fluid the hyperpolarizing effect of UTP is blunted (-11.6 +/- 2.3 mV) and only transient. In conclusion, UTP similar to purine triphosphates hyperpolarizes MDCK cells by increasing the potassium conductance. The activation of potassium channels requires calcium, which is apparently recruited from both intra- and extracellular sources.

Animals↗
PubMed1988

Pertussis toxin-dependent and -independent hormonal effects on cultured renal epithelioid cells.

The present study has been performed to test for the involvement of pertussis toxin-sensitive GTP-binding proteins (G-proteins) in the cellular transduction of hormone-induced activation of potassium channels. In Madin Darby canine kidney (MDCK) cells, a permanent cell line from dog kidney, epinephrine, acetylcholine, bradykinin, serotonin and ATP hyperpolarize the cell membrane by activation of potassium channels. In cells pretreated with pertussis toxin the hyperpolarizations elicited by either acetylcholine or serotonin are completely abolished; that following epinephrine is blunted and only transient. The hyperpolarizing effects of ATP or bradykinin are not affected by pertussis toxin. Thus, in MDCK cells both pertussis toxin-dependent and -independent mechanisms operate in parallel to enhance the potassium conductance of the cell membrane.

Acetylcholine↗
PubMed1988

Effect of acetylcholine on electrical properties of subconfluent Madin Darby canine kidney cells.

To elucidate the effects of acetylcholine on the electrical properties of incompletely confluent Madin Darby canine kidney (MDCK) cells continuous measurements of the potential difference across the cell membrane (PD) were made with conventional microelectrodes during rapid changes of extracellular fluid composition. During control conditions PD averages -48.9 +/- 1.0 mV (n = 51). 1 mumol/l acetylcholine leads to a sustained but reversible hyperpolarization of the cell membrane by -17.9 +/- 0.7 mV (n = 51). Half-maximal effect is observed at some 100 nmol/l. 1 mumol/l atropine does not significantly alter the potential difference across the cell membrane, but abolishes reversibly the hyperpolarizing effect of acetylcholine. Increase of extracellular potassium concentration from 5.4 mmol/l to 20 mmol/l depolarizes the cell membrane by +12.1 +/- 1.1 mV (n = 12) in the absence and by +25.7 +/- 0.9 mV (n = 12) in the presence of acetylcholine. Within 80 s removal of extracellular calcium leads to a depolarization of the cell membrane by +16.2 +/- 3.2 mV (n = 9). In the nominal absence of extracellular calcium acetylcholine leads to a transient hyperpolarization by -13.8 +/- 1.8 mV (n = 9), which can be elicited only once. In conclusion, acetylcholine hyperpolarizes the plasma membrane of MDCK cells by calcium-dependent enhancement of potassium conductance.

Acetylcholine↗
PubMed1988

Extra- and intracellular hydrogen ion-selective microelectrode based on neutral carriers with extended pH response range in acid media.

A series of new neutral hydrogen ion carriers suitable for application in H+-selective microelectrodes is presented. One carrier (ETH 1907) proves to be superior to tridodecylamine currently very much in use. Microelectrodes based on ETH 1907 in an optimized membrane composition exhibit a linear dynamic response function from pH 2 to 9 extended into the acidic range, a response time less than or equal to 5 s, and a resistance of about 35 G omega for a tip diameter of about 1 micron. This makes the electrode suitable for measurements at normal physiological intracellular pH as well as in acid physiological media. Measurements using this microelectrode in proximal tubule cells of isolated perfused frog kidney are presented.

Animals↗
PubMed1988

Electrophysiology of cell volume regulation in proximal tubules of the mouse kidney.

The present study has been designed to test for the influence of cell swelling on the potential difference and conductive properties of the basolateral cell membrane in isolated perfused proximal tubules. During control conditions the potential difference across the basolateral cell membrane (PDbl) is -65 +/- 1 mV (n = 74). Decrease of peritubular osmolarity by 80 mosmol/l depolarizes the basolateral cell membrane by +7.8 +/- 0.5 mV (n = 42). An increase of bath potassium concentration from 5 to 20 mmol/l depolarizes the basolateral cell membrane by +25 +/- 1 mV (n = 11), an increase of bath bicarbonate concentration from 20 to 60 mmol/l hyperpolarizes the basolateral cell membrane by -3.2 +/- 0.5 mV (n = 13). A decrease of bath chloride concentration from 79.6 to 27 mmol/l hyperpolarizes the basolateral cell membrane by -1.8 +/- 0.7 mV (n = 6). During reduced bath osmolarity, the influence of altered bath potassium concentration on PDbl is decreased (delta PDbl = +16 +/- 2 mV, n = 11), the influence of altered bicarbonate concentration on PDbl is increased (delta PDbl = -6.0 +/- 0.8 mV, n = 13), and the influence of altered bath chloride concentration on PDbl is unaffected (delta PDbl = -1.8 +/- 0.6 mV, n = 6). Barium depolarizes the basolateral cell membrane to -28 +/- 2 mV (n = 16). In the presence of 1 mmol/l barium, decrease of peritubular osmolarity by 80 mosmol/l leads to a transient hyperpolarization of the basolateral cell membrane by -5.9 +/- 0.5 mV (n = 16).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Ionic requirement for regulatory cell volume decrease in renal straight proximal tubules.

The present study has been performed to test for the ionic requirement of regulatory cell volume decrease in isolated perfused straight proximal tubules of the mouse kidney. Reduction of peritubular osmolarity from 308 mosmol/l to 228 mosmol/l leads within 0.5 min to cell swelling by 16 +/- 1% (n = 26) of original cell volume (Vo). Within 2 min cell volume (V2) approaches 105 +/- 1% of Vo (n = 26) despite continued exposure to hypotonic bath perfusate. Reexposure of the tubules to isotonic bath perfusate shrinks the cells to 94 +/- 1% of Vo (n = 25). Within 2 min from omission of extracellular bicarbonate and CO2 regulatory cell volume decrease is impaired (V2 = 114 +/- 1% of Vo, n = 14). Similarly, regulatory volume decrease is blunted upon prior removal of extracellular sodium (V2 = 115 +/- 2% of Vo, n = 12). In contrast, regulatory volume decrease is not affected by prior removal of extracellular chloride (V2 = 104 +/- 2% of Vo, n = 9). Regulatory volume decrease is impaired in the presence of 1 mmol/l potassium channel blocker barium (V2 = 120 +/- 4% of Vo, n = 7) and of 1 mmol/l carbonic anhydrase inhibitor acetazolamide (V2 = 111 +/- 2% of Vo, n = 16) but is preserved in the presence of 1 mumol/l chloride channel blocker NPPB (V2 = 105 +/- 2% of Vo, n = 11). In conclusion, regulatory cell volume decrease apparently depends on potassium and bicarbonate, but does not depend on chloride.

Animals↗
PubMed1988

Effects of serotonin on electrical properties of Madin-Darby canine kidney cells.

The present study has been performed to test for the influence of serotonin on the potential difference across the cell membrane (PD) of Madin-Darby canine kidney (MDCK)-cells. Under control conditions PD averages -48.6 +/- 0.6 mV (n = 98). Increasing extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarizes the cell membrane by +6.3 +/- 0.6 mV (n = 6) and +14.1 +/- 1.0 mV (n = 12), respectively. The cell membrane is transiently hyperpolarized to -67.8 +/- 0.8 mV (n = 63) by 1 mumol/l serotonin. In the presence of serotonin, increasing extracellular potassium concentration from 5.4 to 20 mmol/l depolarizes the cell membrane by +26.4 +/- 1.0 mV (n = 11). 1 mmol/l barium depolarizes the cell membrane by +15.7 +/- 1.3 mV (n = 17) and abolishes the effect of step increases of extracellular potassium concentration from 5.4 to 10 mmol/l. In the presence of barium, serotonin leads to a transient hyperpolarization by -26.3 +/- 1.0 mV (n = 16). During this transient hyperpolarization, the cell membrane is sensitive to extracellular potassium concentration despite the continued presence of barium. 10 mumol/l methysergide hyperpolarize the cell membrane by -7.2 +/- 2.0 mV (n = 6). In the presence of 10 mumol/l methysergide, the effect of serotonin is virtually abolished (+0.4 +/- 0.9 mV, n = 6). 1 mumol/l ketanserin, a 5-HT2 receptor blocking agent, ICS 205-930, a 5-HT3 receptor blocking agent, and phentolamine, an unspecific alpha-receptor blocking agent, do not significantly modify the effect of serotonin. In the nominal absence of extracellular calcium, the effect of serotonin is markedly reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Antagonists↗
PubMed1988

Inward rectifier K channels in renal epithelioid cells (MDCK) activated by serotonin.

The present study has been performed to test for the effect of intracellular calcium and of serotonin on the channel activity in patches from subconfluent MDCK-cells. In inside-out patches, inwardly rectifying potassium-selective channels are observed with open probabilities of 0.01 +/- 0.01, 0.24 +/- 0.03 and 0.39 +/- 0.07, at 100 nmol/liter, 1 mumol/liter or 10 mumol/liter calcium activity, respectively. The single-channel slope conductance is 34 +/- 2 pS, if the potential difference across the patch (Vp) is zero, and approaches 59 +/- 1 pS, if Vp is -50 mV, cell negative. In the cell-attached mode, little channel activity is observed prior to application of serotonin (open probability = 0.03 +/- 0.03). If 1 mumol/liter serotonin is added to the bath perfusate, the open probability increases rapidly to a peak value of 0.34 +/- 0.04 within 8 sec. In continued presence of the hormone, the open probability declines to approach 0.06 +/- 0.02 within 30 sec. At zero potential difference between pipette and reference in the bath (i.e., the potential difference across the patch is equal to the potential difference across the cell membrane), the single-channel conductance is 59 +/- 4 pS. In conclusion, inwardly rectifying potassium channels have been identified in the cell membrane of subconfluent MDCK-cells, which are activated to a similar extent by increase of intracellular calcium activity to 1 mumol/liter and by extracellular application of 1 mumol/liter serotonin.

Animals↗
PubMed1988

Inhibition of insulin release in vitro mediated by mononuclear cells from diabetic patients treated with cyclosporin A or placebo.

Anti-beta-cell-specific cell-mediated immunity was studied over a 12-mo period in 65 recently diagnosed diabetic patients randomly receiving either cyclosporin or placebo. Anti-beta-cell cellular immunity was assessed by an in vitro test based on the inhibition of insulin release from cultured rat islet cells by patients' mononuclear cells. This beta-cell-suppressive effect disappeared in cyclosporin A-treated patients within 1 mo and did not reappear during 12 mo of follow-up. Conversely, the suppressive effect persisted unchanged in placebo-treated patients during 12 mo of follow-up. These changes were predictive neither of cyclosporin A-induced remission nor of relapses. Results of the insulin-release inhibition test were not correlated to islet cell autoantibodies or HLA phenotype.

Adolescent↗
PubMed1987

Potassium conductance in straight proximal tubule cells of the mouse. Effect of barium, verapamil and quinidine.

The present study has been performed to test for the influence of verapamil and quinidine on the potential difference across the basolateral cell membrane (PDbl) and on the basolateral potassium conductance of isolated perfused segments of the mouse proximal tubule. PDbl was recorded continuously with conventional microelectrodes during rapid alterations of bath or luminal perfusate composition. The contribution of the basolateral potassium conductance to the conductance of both cell membranes (tk) was estimated from the effects of altered bath potassium concentration on PDbl. Under control conditions tk approaches 0.8, i.e. the basolateral cell membrane is mainly conductive to potassium. Neither quinidine nor verapamil affect PDbl at concentrations below 10 mumol/l. At higher concentrations both substances depolarize the basolateral cell membrane mimicking the effect of 1 mmol/l barium. In the presence of 0.1 mmol/l verapamil tk is virtually abolished at 5 to 10 mmol/l bath potassium concentration but is almost unaffected at bath potassium concentrations between 20 and 40 mmol/l. 1 mumol/l ionophore A-23187 does not change the depolarizing effect of 0.1 mmol/l verapamil on cell membrane potential. In the presence of 0.1 mmol/l quinidine, tk is reduced to some 50%, irrespective of the bath potassium concentration. It is concluded that the potassium conductance in straight proximal tubules is inhibited not only by barium but as well by high concentrations of verapamil and quinidine. The effect is probably direct and not related to alterations in the intracellular calcium activity.

Animals↗
PubMed1987

Amino acid sequence of the cytochrome subunit of the photosynthetic reaction centre from the purple bacterium Rhodopseudomonas viridis.

The complete nucleotide sequence of the gene encoding the cytochrome subunit of the photosynthetic reaction centre from the purple bacterium Rhodopseudomonas viridis, and the derived amino acid sequence are presented. The nucleotide sequence of the gene reveals the existence of a typical bacterial signal peptide of 20 amino acid residues which is not found in the mature cytochrome subunit. The gene encoding the cytochrome subunit is preceded by the gene encoding the M subunit. Both genes overlap by 1 bp. The mature cytochrome subunit consists of 336 amino acid residues; 73% of its amino acid sequence was confirmed by protein sequencing work. The mol. wt of the cytochrome subunit including the covalently bound fatty acids and the bound heme groups is 40 500. The internal sequence homology is low, despite the symmetric structure of the cytochrome subunit previously shown by X-ray crystallographic analysis of the intact photosynthetic reaction centre. Sequence homologies to other cytochromes were not found.

Journal Article↗
PubMed1987

Effects of bradykinin on electrical properties of Madin-Darby canine kidney epithelioid cells.

In the present study we have investigated the influence of bradykinin on the potential difference across the cell membrane (PD) of Madin Darby Canine Kidney (MDCK)-cells. In the absence of bradykinin PD averages -52.6 +/- 0.9 mV (n = 52). Increasing extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarizes the cell membrane by +5.2 +/- 0.3 mV (n = 8) and +14.9 +/- 1.0 mV (n = 9), respectively. The application of 0.1 mumol/l bradykinin leads to a transient hyperpolarization of the cell membrane to -70.3 +/- 0.6 mV (n = 30). During this transient hyperpolarization increasing extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarizes the cell membrane by +10.4 +/- 0.7 mV (n = 10) and +29.2 +/- 0.8 mV (n = 8) respectively. Application of fragments of bradykinin (0.1 mumol/l) are without significant effect on the potential difference across the cell membrane. 1 mmol/l barium depolarizes the cell membrane by +15.8 +/- 1.2 mV (n = 9) and abolishes the effect of step increase of extracellular potassium concentration from 5.4 to 10 mmol/l. In the presence of barium, bradykinin leads to a transient hyperpolarization by -24.7 +/- 1.3 mV (n = 7). During this transient hyperpolarization, the cell membrane is sensitive to extracellular potassium concentration despite the continued presence of barium. In the nominal absence of extracellular calcium, bradykinin leads to a transient hyperpolarization, which can be elicited only once. The transient hyperpolarization is not affected by the presence of verapamil or indomethacin. In conclusion, bradykinin hyperpolarizes MDCK-cells by increasing the apparent potassium conductance.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Epinephrine activates outward rectifying K channel in Madin-Darby canine kidney cells.

Patch-clamp recordings were used to study the epinephrine dependent activation of ion channels in the cell membrane of cultured subconfluent renal epithelial (MDCK) cells. The patch-current was dominated by two populations of K channels. The spontaneously active population of K channels shows an inward rectifying behavior. Addition of epinephrine to the cell exterior, after the patch-pipette had been sealed to the cell membrane, increased the open probability of the inward rectifying K channel and shifted the membrane potential in the hyperpolarizing direction. The epinephrine induced hyperpolarization occurs in the range of seconds and is caused by activation of outward-rectifying K channels. The outward-rectifying K channel could not be observed under control conditions. Epinephrine activated channels always appeared in clusters of four to nine channels. Both populations of K channels are modulated in their open probability by cytoplasmic free calcium and voltage.

Animals↗
PubMed1987

Electrical properties of Ehrlich ascites tumor cells.

The cell membrane potential (PD) of Ehrlich ascites tumor cells was measured continuously at 37 degrees C with conventional microelectrodes during rapid alterations of extracellular fluid composition. At extracellular electrolyte composition mimicking the in vivo situation PD is -56.7 +/- 0.7 mV and the apparent membrane resistance is 62.2 +/- 2.2 M omega. Increasing extracellular potassium concentration from 5.4 to 20.0 mmol/l depolarizes the cell membrane by +18.4 +/- 0.5 mV. Thus, the transference number for potassium (tk, apparent slope potassium conductance over slope membrane conductance) is 0.53 +/- 0.01. A significant correlation is observed between tk and PD: tk = -(0.014 +/- 0.001) [1/mV] X PD [mV] -(0.243 +/- 0.051). 0.7 mmol/l barium depolarizes the cell membrane by +28.2 +/- 0.7 mV, increases the apparent membrane resistance by a factor of 2.6 +/- 0.1 and abolishes the apparent potassium conductance. Reduction of extracellular sodium concentration from 141 to 21 mmol/l depolarizes the cell membrane by +3.1 +/- 1.3 mV. Similarly, 0.1 mmol/l amiloride depolarizes the cell membrane by +3.3 +/- 0.7 mV. Reduction of extracellular chloride concentration from 128 to 67 mmol/l hyperpolarizes the cell membrane by -2.5 +/- 0.2 mV. 1 mmol/l anthracene-9-COOH does not significantly alter PD. Temporary omission of glucose from the extracellular fluid has no appreciable effect on PD. In conclusion, PD of Ehrlich ascites tumor cells is in the range of other mammalian epithelial cells and is generated mainly by potassium diffusion, while the conductances to sodium and chloride appear to be small.

Animals↗