The effects of external cations and ouabain on the intracellular sodium activity of sheep heart Purkinje fibres
- 1 December 1977
- journal article
- research article
- Published by Wiley in The Journal of Physiology
- Vol. 273 (1), 211-240
- https://doi.org/10.1113/jphysiol.1977.sp012090
Abstract
The intracellular Na activity of sheep heart Purkinje fibers was measured using recessed-tip Na+-sensitive glass micro-electrodes. The internal Na activity was 7.2 .+-. 2.0 mM (mean .+-. SD, n = 32) at the normal external Na concentration, [Na]o, in these experiments of 140 mM (equivalent to an external Na activity of 105 mM). The equilibrium potential for Na across the fiber membrane was therefore approximately +70 mV. When the [K]o was altered the internal Na activity changed, reaching a new level within about 20 min. Increasing the [K]o from 4 to 25 mM decreased the internal Na by approximately 30%, while decreasing the [K]o from 4 to 1 mM increased internal Na by 20%. The removal of external K produced an easily reversible increase in the internal Na with an initial rate equivalent to a concentration change of 0.24 .+-. 0.07 m-mole/min (mean .+-. SD, n = 8). Ouabain produced increases in the internal Na activity that were only very slowly reversible. The threshold concentration for producing an increase was approximately 10-7 M. When [Na]o was reduced the internal Na activity fell rapidly with a single exponential time course (time constant 3.3 .+-. 0.8 min, mean .+-. SD, n = 16) to a new, relatively stable level. The recovery of internal Na on return to the normal [Na]o did not have a simple time course. It was normally complete within 10-30 min. The relationship of the stabilized level of the internal Na activity to the [Na]o was approximately linear over the range 140-14 mM-[Na]o. When [Na]o was reduced from 140 to 14 mM the internal Na activity fell by 72 .+-. 5% (mean .+-. SD, n = 21). When the [Na]o was reduced, the decrease in the internal Na activity was partially inhibited by Mn or by removal of external Ca. When the [Ca]o was altered over the range 0.2-16 mM the internal Na activity was reduced by approximately 50% for a 10-fold increase in the [Ca]o. The relationship between internal Na and contractility is discussed.This publication has 47 references indexed in Scilit:
- The effect of external Na and amiloride on pHi recovery in mouse soleus muscle [proceedings].1977
- The effect of extracellular potassium on the intracellular potassium ion activity and transmembrane potentials of beating canine cardiac Purkinje fibers.The Journal of general physiology, 1977
- The effect of lowering external sodium on the intracellular sodium activity of crab muscle fibres.The Journal of Physiology, 1977
- Binding sites related to ouabain-induced stimulation or inhibition of the sodium pumpNature, 1977
- Direct measurement of the intracellular pH of mammalian cardiac muscle.The Journal of Physiology, 1976
- Two levels of resting potential in canine cardiac Purkinje fibers exposed to sodium-free solutions.Circulation Research, 1976
- CT of Primary and Secondary Craniocerebral Neuroblastoma1976
- Effects of Na and K ions on the active Na transport in guinea-pig auriclesPflügers Archiv - European Journal of Physiology, 1976
- Proceedings: The influence of low doses of ouabain and potassium ions on sheep Purkinje fibre contractility.1975
- Activities of potassium and sodium ions in rabbit heart muscle.The Journal of general physiology, 1975