Biomedical subjects

L Leybaert

Publications and source records attributed to L Leybaert.

23 records · Page 2Linked to original sources

PubMed1994

Intracellular pH changes during zona drilling.

OBJECTIVE: To investigate whether zona drilling of oocytes, a technique used to locally disrupt the zona pellucida, causes important changes in intracellular pH. DESIGN AND METHODS: In a first set of experiments, intracellular pH was measured during zona drilling of mouse oocytes, using pH-sensitive microelectrodes. In a second set of experiments human oocytes that failed to fertilize were used to measure intracellular pH during drilling. In these cells intracellular pH was measured using microfluorimetry with the pH-sensitive dye 2',7'-bis-carboxyethyl-5(6)-carboxyfluorescein. RESULTS: In mouse oocytes intracellular pH dropped from 7.25 +/- 0.02 (mean +/- SEM) to 7.09 +/- 0.03 during zona drilling, followed by a recovery to pH 7.17 +/- 0.02 after 4 minutes (n = 20). In human oocytes, intracellular pH dropped over 0.36 +/- 0.10 pH units during drilling, followed by a recovery that was complete within 4 minutes (n = 14). CONCLUSION: Zona drilling is associated with a significant cytoplasmic acidification both in mouse and human oocytes. This effect is perhaps related to the high incidence of cytoplasmic degeneration after zona drilling of human oocytes.

Animals↗

PubMed1993

Effects of flunarizine on induced calcium transients as measured in fura-2-loaded neurons of the rat dorsal root ganglion.

The effect of the calcium entry blocker flunarizine on a high-potassium induced increase of intracellular free calcium was studied. The experiments were done with neurons isolated from rat dorsal root ganglia and loaded with the calcium-sensitive dye fura-2. The increase of calcium induced by 60 mmol/l potassium was abolished after removal of extracellular calcium, was reversibly reduced by 50 mumol/l cadmium (76% inhibition), 50 mumol/l nickel (25% inhibition) and 10 mumol/l nifedipine (18% inhibition), and reversibly increased after removal of extracellular sodium (26% increase). The potassium induced increase of intracellular calcium is, therefore, mediated by transmembrane calcium influx, probably to a large extent through cadmium-sensitive calcium channels. Flunarizine (5 min incubation followed 1 min wash-out) reduced the amplitude of the high-potassium induced calcium increase in a dose-dependent manner (Kd = 370 +/- 100 nmol/l; mean +/- SEM; n = 8), causing complete inhibition at a concentration of 10 mumol/l in the majority of cells. Flunarizine (> or = 1 mumol/l) caused a reversible increase of the resting level of intracellular calcium in some cells, an effect which disappeared in the absence of extracellular calcium. The drug (1 mumol/l had no influence on the time course of recovery of intracellular calcium subsequent to a rise induced by high-potassium or by the calcium ionophore A23,187. It is concluded that flunarizine acts as an inhibitor of depolarization-mediated calcium influx. At a concentration of 1 mumol/l, the drug presumably has no effect on cellular calcium extrusion and/or sequestration mechanisms.

Animals↗

PubMed1993

Effect of flunarizine and methylprednisolone on functional recovery after experimental spinal injury.

The effect of flunarizine and methylprednisolone on the recovery of somatosensory evoked potentials (SEPs) was evaluated in an experimental model of spinal cord impact injury in anesthetized cats. In addition, the effect of flunarizine on posttraumatic spinal cord blood flow (SCBF) (using the hydrogen clearance technique) and interstitial calcium and potassium activity (ion-selective electrodes) was investigated. After the injury (600 g.cm), SEPs disappeared, followed by a spontaneous recovery to 17% of the preinjury amplitude at the end of the 4 h observation period. Flunarizine treatment (0.1 mg/kg IV, given 5 and 120 min after injury) resulted in a significantly improved recovery of SEPs, reaching 52% of the preinjury amplitude. Methylprednisolone treatment (30 mg/kg IV, given 5 min after injury) resulted in a 30% recovery level, significantly better than in untreated animals but significantly inferior to flunarizine treatment. Combination of both treatments resulted in a 62% recovery level, significantly better than after methylprednisolone treatment alone. Flunarizine treatment had no significant effect on the postinjury evolution of SCBF and interstitial potassium activity; it did, however, significantly accelerate the recovery of interstitial calcium activity, which sharply decreased immediately after injury. It is concluded that intravenous administration of the calcium entry blocker flunarizine improves the functional recovery of the spinal cord in the acute phase after experimental spinal impact injury. The observed improvement is not achieved by an effect on local blood flow but is possibly related to an inhibitory effect of the drug on cellular calcium entry.

Animals↗

PubMed1989

Simulated ischemia and intracellular pH in isolated ventricular muscle.

Isolated guinea pig papillary muscles were subjected to an in vitro model of ischemia, consisting of superfusion arrest and immersion in paraffin oil, which results in restriction of substrate supply and metabolite washout. Intracellular pH (pHi) and surface pH (pHs) were measured with glass microelectrodes. Contractile force declined to 82% of the pre-"ischemic" value after 2 min and to 37% of the control value after 10 min. In addition, a shortening of the time to peak and duration of contraction was noted. The rate of force development decreased later than the rate of relaxation. After 10 min, pHi was acidified on average 0.08 pH unit, which is about one-third of the measured pHs change. Tripling the ischemic pHi change by reduction of the intracellular buffering power only slightly increased the rate of tension decline. Experimental pHi changes of similar magnitude, induced during normal superfusion, had a smaller effect on contractile force and failed to reproduce the characteristic changes in time course of the contraction. It is concluded that, in our condition of simulated ischemia, the intracellular acidification cannot account fully for the rapid decline in contractility.

Amiloride↗

PubMedDate not supplied

A voltage-clamp study of calcium currents in neurons freshly isolated from the dorsal root ganglion of adult rats.

Calcium currents were studied in a preparation of freshly isolated neurons of the dorsal root ganglion (DRG) of adult rats using the whole-cell voltage-clamp technique in conditions of minimal current flow through sodium and potassium channels. A low-threshold (LT) and a high-threshold (HT) current were distinguished on the basis of a different potential of activation. Both currents also showed differences in their peak amplitude, their distribution among the cells, their kinetics, their steady-state inactivation curve and their sensitivity to cadmium. Comparison of the properties of both currents with the known properties of calcium currents in DRG neurons from immature animals indicates a slower rate of inactivation of the LT-current in the adult DRG neuron. The calcium entry blocker flunarizine (10 microM) caused a negative shift of the steady-state inactivation curve of the inactivating component of HT-current, an effect which suggests voltage-dependent inhibition.

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