Chapter-1 / Physiological Foundations - WHNLive Public Library

are triggered. At the same site, howvr, there i al 0 a main effect area of the tissue connected with this (increase of 11 aand the increase of the O 2 transport 002MT . An improvement in the deficient situationin the venou upply area of the capillary cell destruction far back and often allow a re­blood flow) after 02MT, shift the border ofby m an of rai ing the P0 2 - art is, however, filling of the areas put out of action after O2trictly limited, because this rise benefits the deficiency, by means of cell division and cellart rial area of the capillary more by far (cf. migration.Fig. 3). But the lasting drop in the P0 2 oven1.4.4 Change in the cell metabolism from respiration to fermentationIn increasing O 2 deficiency the cell is forced tocover its energy deficit by glycolysis (Paragraph1.4.2). Due to the energy yield of fermentationmetabolism being only 7 % compared with respiration,glycolysis increases very quicklybelow a certain POz level. It is therefore usualto speak of a sudden change in the cell metabolism.In [146]Po 2=5mmHg (0.6 kPa) is givenas a critical level for the change from respirationto fermentation. Because of the significanceof this figure for the over-acidification oftissue areas affected by O 2 deficiency, discussedin the following paragraph, it seemed worthdetermining directly the critical P0 2level in aspecially constructed Po 2 /pH in vitro measurementarrangement with high sensitivity [146].For this the hearts of I to 2-day-old, or adult,rats were homogenized in an ice-cold bicarbonate-freeKrebs-Ringer solution (KR) or inlactalbumin-yeast medium (LV), and incubatedin the named solutions containing 200-100 mgt100 ml glucose in vessels of the type describedin Fig. 100 [188,189], at T = 37°C; pH andP0 2 were continuously recorded, the startinglevels being adjusted to pH = 7 and POz =9-14 mmHg (1.2-19.7 kPa). The pH was continuouslyre-adjusted by adding 0.1 N aOH,the adjustment of the PO z achieved with z/O 2 mixtures having a defined composition.Before measurement was begun, the vessel wascompletely filled with the tissue suspension (noheadspace). For the measurement of the POzw~ used an electrode developed in our institute.The measurement of the drop in POz, caused bycell respiration of the myocardial tissue in theKrebs-Ringer solution is given in Fig. 101. Therespiration rate here falls from higher levels atP02 = 45 mmHg (6 kPa) to zero, when POz =1 mmHg (0.13 kPa) is reached. At the timepointt = 155 min oxygen was added again, somuch that the P0 2 level in the solution roseagain from I to 6 mmHg (0.8 kPa). Despite thepreceding deficiency condition of approximately20 min duration, the myocardiac cellsfIOl- eI~C'trode/"SSurt-comjlt'llSO!ingcopllorypH cOlI/podgloss electrodechorging connulo with tap...l..-J.l>-H-t-- stopptrolr-It!Jl!llld~:t:l~~;;;-- rent Yolre50m1f7Fig. 100 Incubation \IIssel for the measurementof respiration and acidification (glycol •sis) of myocardiac cells as a function of thePO z le\lll