Modification of the after-potential of single muscle fibres by 2:4-dinitrophenol

INTRACELLULAR recording of electrical activity in the excised sartorius muscle of Hyla coerulea shows a negative after-potential of 20-25 mV. with a half-time of decay (t1) of 8-12 m.sec. at 25°C. The time of recovery to resting potential level is increased to t1/2 of 18-25 m.sec. when K+ is absent from the glucose-phosphate-Ringer medium. Successive Increases of K+ concentration up to 15 N/1,000 cause successive shortenings of repolarization time to t1 6 m.sec.1. These processes are faster by one-third in Rana catesbiana. The after-potential of Hyla muscle is prolonged, also, by reduction of Na+ in the medium to 20 M (t1/2 15-20 m.sec.) or by increase of H+ to pH. 6.5, which gives t1 of 28 m.sec

Heat, salt and hormones in panting and sweating animals

IN hot climates sweating or panting to provide evaporative cooling are required for the survival of mammals. The loss of extracellular water is linked with cell water exchanges, renal water-saving, adjustments of salt excretion and hormone production

Extracellular fluid distribution in tropical merino sheep

Merino ewes and wethers maturing from 12 to 53 months of age were studied for 3 1/2 years in the field at Julia Creek (lat. 21° S.) during summer and winter. Measurements were made of plasma volume and extracellular volume, plasma proteins, haemoglobin, haematocrit, and plasma electrolytes. The range of normal in apparently healthy sheep was found to be very wide. Large changes took place in the fluid volumes during the period of investigation; the changes appeared to be independent of seasons but to a great extent determined by nutrition. Poorly nourished sheep as a whole had increased extra- cellular fluid space, and the space shrank again on improved pasture. Age and sex did not influence the fluid volumes. Lactation was associated with an increase in fluid spaces, and yard feeding with a decrease. Non-tropical sheep introduced from lat. 30° S. during winter had similar fluid volumes to the tropical sheep when investigated 2 months after their arrival. Tropical Merinos at any age or season had larger plasma volumes than sheep kept in laboratory pens in Brisbane or in Melbourne