Biomedical subjects

M P Janssen

Publications and source records attributed to M P Janssen.

4 recordsLinked to original sources

PubMed1992

Effect of membrane fluidity and fatty acid composition on the prothrombin-converting activity of phospholipid vesicles.

Vesicles composed of phospholipids with different fatty acyl side chains have been utilized to examine the importance of the nonpolar membrane region for the prothrombin-converting activity of procoagulant phospholipid vesicles. Membranes composed of phosphatidylserine (PS) and phosphatidylcholine (PC) with unsaturated fatty acyl side chains were more active in prothrombin activation than membranes composed of phospholipids with saturated fatty acyl chains. This phenomenon was observed above the phase transition temperature, i.e., on membranes in the liquid-crystalline state. The prothrombin-converting activity of saturated phospholipids approached the activity of unsaturated phospholipids at high factor Va concentrations, which is indicative for a less favorable equilibrium constant for prothrombinase assembly on membrane surfaces composed of saturated phospholipids. The difference between saturated and unsaturated phospholipids was annulled on membranes with high mole percentages of PS. This may result from a compensating contribution of electrostatic forces to the binding equilibria involved in prothrombinase assembly. Additional effects on the prothrombin-converting activity were observed when membranes containing saturated phospholipids were studied below their phase transition temperature. In agreement with Higgins et al. [(1985) J. Biol. Chem. 260, 3604-3612], we found that the time required for the assembly of prothrombinase from membrane-bound factors Xa and Va is considerably prolonged on solid membranes. However, we also observed an effect of membrane fluidity on the steady-state rate of prothrombin activation. Kinetic experiments at saturating factor Va concentrations showed that the transition from the liquid-crystalline to the gel state caused a more than 9-fold decrease of the kcat of prothrombin activation without affecting the Km for prothrombin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Statistical methods used in the marathon study.

In this note an outline is given of the statistical methods which were used in the marathon study. The techniques are: box-and-whisker plots, several nonparametric tests, and methods for assessing the intraindividual variations and critical differences.

Adaptation, Physiological↗

PubMed1989

Plasma activity of muscle enzymes: quantification of skeletal muscle damage and relationship with metabolic variables.

One hundred fourteen sedentary volunteers (34 +/- 8 years) took part in an endurance training study to be completed after 18-20 months with a marathon. Ultimately, 60 males and 18 females achieved that goal. The training program, carefully supervised, was divided into three periods with a maximum of 45-, 70-, and 110-km week training volume and concluded with a performance race of 15, 25, and 42.2 km, respectively. Three days before and 3 and 5 days after each race, 35 subjects were selected to perform a progressive treadmill test and the remaining subjects participated in field tests of 400 and 1000 m. A significant decrease in half-life time of CK enzyme plasma activity after running long distances in the course of the study from 20 h to 13 h was observed. Based on plasma enzyme activity and supposing that the total enzyme content left the muscle fiber, the estimated amount of muscle damage was found to be small. A gender difference in plasma enzyme activity increase (females demonstrated a lower increase) occurred only after the marathon.

Adaptation, Physiological↗

PubMed1989

Occurrence of running injuries in adults following a supervised training program.

To study the occurrence of running-related injuries, a group of 115 volunteers were supervised in a training program. These subjects who had limited or no running experience were asked to keep a diary in which they registered information on the training program and injuries. Ultimately, 63% of the diaries fulfilled the criteria for inclusion into longitudinal analysis. The training program (18-20 months) consisted of three phases, each phase finished with a contest (15 km, 25 km, and a marathon, respectively). The participants were individually supervised by an experienced coach with special attention to physiologic training and injury-preventive aspects. Eighty-five percent (n = 62) of the research population sustained at least one injury during the experiment. They reported in total 174 injuries. The number of injury cases per week increased gradually over the experimental period; however, when expressed per unit of exposure time (i.e., 1000 training hours), it showed a decline. There was a significant correlation between the number of injured volunteers and the distance covered during the training at the start of the training program. The anatomic distribution of the injuries is in agreement with findings in the literature. There was also a possible preference for the localization of injuries to the lower leg and Achilles tendon on the left side of the body.

Adult↗