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R D Keynes

Publications and source records attributed to R D Keynes.

82 records · Page 5Linked to original sources
PubMed1966

Observations on the potential across the rumen of the sheep.

1. The electric potential difference between rumen contents and jugular venous blood was measured in anaesthetized sheep. In order to investigate the effect on the potential of changing the ionic concentrations within the rumen, the digesta were removed from the rumen and various salt solutions were substituted. The reticulo-rumen sac was isolated before the experiment by ligation of the oesophagus and the reticulo-omasal junction. 2. The observation of Dobson & Phillipson (1958) that the rumen contents are normally of the order of 30 mV negative to the blood was confirmed. 3. For potassium concentrations between 25 and 100 mM the potential at constant [Na+] varied linearly with log [K+]. With sulphate as the anion, the slope for a 10-fold concentration change was 39.7 +/- 3.0 mV when [Na+] was around 50 mM. The slope showed a tendency to increase when [Na+] was lowered, and to decrease when [Na+] was raised. 4. When chloride was substituted for sulphate, both the slope and the absolute size of the potential were slightly reduced. 5. When the sodium concentration was varied at constant [K+], the potential increased as an approximately linear function of [Na+]. At around 10 mM-K the mean slope was 0-32 +/- 0.07 mV/mM; at the highest potassium concentrations it fell to 0-13 +/- 0 05 mV/mM. 6. In most of these experiments isotonicity was maintained with sucrose. The results of a few tests in which Li+ was substituted for Na+ or K+ suggested that the rumen epithelium behaves in a relatively inert fashion towards this ion.

Animals↗
PubMed1966

The potential and short-circuit current across isolated rumen epithelium of the sheep.

1. A technique is described for working with isolated sheets of rumen epithelium. Epithelium was obtained at operations for rumen fistulation or in acute experiments and was rapidly mounted between two cone-shaped chambers each of which held 40 ml. of bathing fluid. The fluids were gassed with 95% O2/5% CO2 and 20 cm2 of epithelium was exposed to the fluids. 2. Electrical measurements were made of (a) the potential generated across the epithelium, (b) the short-circuit current which flowed and (c) the resistance of the epithelium. 3. The results are grouped according to the composition of the sheep Ringer solution used to bathe the epithelium. The most stable preparation was obtained when the solutions contained 5 mM each of glucose, acetate, propionate and butyrate as well as bicarbonate and phosphate buffers. 4. In Cl- media, the average initial p.d., short-circuit current (s.-c.c.) and resistance were 9.3 mV, 11.6 microA/cm2 and 1156 omega x cm2 respectively. Higher values of 17.6 mV, 17.3 microA/cm2 and 1501omega x cm2 were recorded in SO4(2-) media. In both media, the s.-c.c. declined at approximately 1.5 microA/cm2. hr and preparations were suitable for study over periods from 4 to 6 hr. 5. When the concentration of potassium was varied on either side of the epithelium at constant [Na+], the potential showed a linear relation with log [K+] for both sides of the epithelium. 6. Changing the sodium concentrations at constant [K+] on either side of the epithelium caused negligible alterations in the potential. 7. Exclusion of sodium from the media bathing both sides of the epithelium abolished the potential and s.-c.c. 8. The addition of ouabain to the blood side of the preparation abolished the potential and s.-c.c. whereas on the rumen side these parameters were unaffected.

Animals↗
PubMedDate not supplied

The role of giant axons in studies of the nerve impulse.

The large size of the individual axons in the motor nerves of certain invertebrates has facilitated technical approaches that were not feasible elsewhere. A brief account is given of the way in which giant axons have taken and held the lead in research on the mechanism of conduction.

Animals↗