Ionic currents in two strains of rat anterior pituitary tumor cells

J. M. Dubinsky, G. S. Oxford

Research output: Contribution to journalArticle

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Abstract

The ionic conductance mechanisms underlying action potential behavior in GH3 and GH4/C1 rat pituitary tumor cell lines were identified and characterized using a patch electrode voltage-clamp technique. Voltage-dependent sodium, calcium, and potassium currents and calcium-activated potassium currents were present in the GH3 cells, GH4/C1 cells possess much less sodium current, less voltage-dependent potassium current, and comparable amounts of calcium current. Voltage-dependent inward sodium current activated and inactivated rapidly and was blocked by tetrodotoxin. A slower-activating voltage-dependent inward calcium current was blocked by cobalt, manganese, nickel, zinc, or cadium. Barium was substituted for calcium as the inward current carrier. Calcium tail currents decay with two exponential components. The rate constant for the slower component is voltage dependent, while the faster rate constant is independent of voltage. An analysis of tail current envelopes under conditions of controlled ionic gradients suggests that much of the apparent decline of calcium currents arises from an opposing outward current of low cationic selectivity. Voltage-dependent outward potassium current activated rapidly and inactivated slowly. A second outward current, the calcium-activated potassium current, activated slowly and did not appear to reach steady state with 185-ms voltage pulses. This slowly activating outward current is sensitive to external cobalt and cadmium and to the internal concentration of calcium. Tetraethylammonium and 4-aminopyridine block the majority of these outward currents. Our studies reveal a variety of macroscopic ionic currents that could play a role in the initiation and short-term maintenance of hormone secretion, but suggest that sodium channels probably do not make a major contribution.

Original languageEnglish
Pages (from-to)309-339
Number of pages31
JournalJournal of General Physiology
Volume83
Issue number3
StatePublished - 1984
Externally publishedYes

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Pituitary Neoplasms
Calcium
Potassium
Sodium
Cobalt
Tail
4-Aminopyridine
Tetraethylammonium
Sodium Channels
Tetrodotoxin
Patch-Clamp Techniques
Barium
Manganese
Tumor Cell Line
Nickel
Cadmium
Action Potentials
Zinc
Electrodes
Hormones

ASJC Scopus subject areas

  • Physiology

Cite this

Ionic currents in two strains of rat anterior pituitary tumor cells. / Dubinsky, J. M.; Oxford, G. S.

In: Journal of General Physiology, Vol. 83, No. 3, 1984, p. 309-339.

Research output: Contribution to journalArticle

Dubinsky, JM & Oxford, GS 1984, 'Ionic currents in two strains of rat anterior pituitary tumor cells', Journal of General Physiology, vol. 83, no. 3, pp. 309-339.
Dubinsky, J. M. ; Oxford, G. S. / Ionic currents in two strains of rat anterior pituitary tumor cells. In: Journal of General Physiology. 1984 ; Vol. 83, No. 3. pp. 309-339.
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