A comparison of ion concentrations, potentials and conductances of amphibian, bovine and cephalopod lenses

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Abstract

The concentrations of sodium, potassium and chloride in frog and bovine lenses showed a normal intracellular ion distribution with the sum of the internal cations approximately equal to the external sum. In the cephalopod lens, however, the sum inside was much lower than that outside. The membrane potentials of frog, Sepiola and bovine lenses were -63, -63 and -23 mV respectively. A comparison of the electrical data with the Nernst potentials predicted from ion concentration data indicated that sodium and chloride ions as well as potassium contributed to the membrane potential in frog and bovine. In contrast, the membrane and Nernst potentials for potassium were equal in Sepiola. Substituting potassium for sodium in the external medium depolarized lens potentials in all three species. Estimates of the relative permeabilities of sodium, potassium and chloride were obtained by fitting the Goldman Hodgkin Katz equation to the potential data. The potassium permeability was determined directly by 42K efflux measurements and values of 2.99, 9.83 and 3.13 (x-8m sec-1) were obtained for frog, Sepiola and bovine lenses respectively. The effect of raising external potassium on the efflux rate constant was determined and there was reasonable agreement between experiment and theory (Kimizuka-Koketsu) in frog and bovine lenses, but the Sepiola data indicated that the potassium permeability decreased by a factor of 2.6 when the external potassium was raised from 10 to 120 m(M) K+. The measured specific conductances, obtained using two internal micro electrodes, were 7.7, 15.9 and 9.9 (Sm-2) for frog, cephalopod and bovine lenses respectively. These data compare with computer (Kimizuka Koketsu theory) of 7.5, 14.1 and 17.2 (Sm-2). The effect of increasing external potassium on the conductance was also tested and there was good agreement between experiment and theory (assuming constant permeabilities) only in the amphibian lens. However, when the cephalopod data were corrected assuming a 2.6 fold decrease in P(K) for a twelvefold increase in potassium, then there was excellent agreement between experiment and theory. The bovine measured conductances were much lower than the theoretical values throughout the range of external potassium concentrations and several explanations were proposed to account for the discrepancies.

Original languageEnglish (US)
Pages (from-to)167-186
Number of pages20
JournalJournal of Physiology
Volume272
Issue number1
StatePublished - 1977
Externally publishedYes

Fingerprint

Cephalopoda
Amphibians
Lenses
Potassium
Ions
Anura
Permeability
Sodium Chloride
Membrane Potentials
Potassium Chloride
Cations
Electrodes
Sodium

ASJC Scopus subject areas

  • Physiology

Cite this

A comparison of ion concentrations, potentials and conductances of amphibian, bovine and cephalopod lenses. / Delamere, Nicholas A; Duncan, G.

In: Journal of Physiology, Vol. 272, No. 1, 1977, p. 167-186.

Research output: Contribution to journalArticle

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abstract = "The concentrations of sodium, potassium and chloride in frog and bovine lenses showed a normal intracellular ion distribution with the sum of the internal cations approximately equal to the external sum. In the cephalopod lens, however, the sum inside was much lower than that outside. The membrane potentials of frog, Sepiola and bovine lenses were -63, -63 and -23 mV respectively. A comparison of the electrical data with the Nernst potentials predicted from ion concentration data indicated that sodium and chloride ions as well as potassium contributed to the membrane potential in frog and bovine. In contrast, the membrane and Nernst potentials for potassium were equal in Sepiola. Substituting potassium for sodium in the external medium depolarized lens potentials in all three species. Estimates of the relative permeabilities of sodium, potassium and chloride were obtained by fitting the Goldman Hodgkin Katz equation to the potential data. The potassium permeability was determined directly by 42K efflux measurements and values of 2.99, 9.83 and 3.13 (x-8m sec-1) were obtained for frog, Sepiola and bovine lenses respectively. The effect of raising external potassium on the efflux rate constant was determined and there was reasonable agreement between experiment and theory (Kimizuka-Koketsu) in frog and bovine lenses, but the Sepiola data indicated that the potassium permeability decreased by a factor of 2.6 when the external potassium was raised from 10 to 120 m(M) K+. The measured specific conductances, obtained using two internal micro electrodes, were 7.7, 15.9 and 9.9 (Sm-2) for frog, cephalopod and bovine lenses respectively. These data compare with computer (Kimizuka Koketsu theory) of 7.5, 14.1 and 17.2 (Sm-2). The effect of increasing external potassium on the conductance was also tested and there was good agreement between experiment and theory (assuming constant permeabilities) only in the amphibian lens. However, when the cephalopod data were corrected assuming a 2.6 fold decrease in P(K) for a twelvefold increase in potassium, then there was excellent agreement between experiment and theory. The bovine measured conductances were much lower than the theoretical values throughout the range of external potassium concentrations and several explanations were proposed to account for the discrepancies.",
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