Calcium-dependent slow potassium conductance in rat skeletal myotubes

John Barrett, Ellen Barrett, Lori B. Dribin

Research output: Contribution to journalArticle

52 Citations (Scopus)

Abstract

A prolonged hyperpolarizing afterpotential (amplitude 5-20 mV, half decay time about 400 msec at 25°C) follows the action potential in myotubes and myosacs cultured from rat skeletal muscle. This slow hyperpolarizing afterpotential (hap) is mediated by an increase in membrane K conductance, because its reversal potential follows the Nernst potential for K and is not affected by other ions. The conductance increase measured during the hap (up to four times the resting input conductance) correctly predicts the time course of the slow hap. The slow hap is Ca dependent. Its amplitude decreases when bath [Ca] is lowered, and both amplitude and duration increase when bath [Ca] is raised. The slow hap is blocked by intracellular injection of the calcium chelator, EGTA. It is inhibited by solutions containing 2-4 mM manganese or 1-5 mM barium, but is not blocked by 5-20 mM tetraethylammonium. Myotubes bathed in zero [Na], high [Ca] solutions show calcium action potentials, which are inhibited by 2-10 mM manganese, nickel or cobalt. Myotubes bathed in isotonic Ca salts (or in 2 mM Ca plus 5 mM caffeine) show long-lasting (up to 10 sec) spontaneous hyperpolarizations accompanied by prolonged contractions. These hyperpolarizations are associated with a large increase in input conductance, and they reverse in sign near the K equilibrium potential. They appear to reflect activation of the Ca-sensitive K conductance by Ca released from intracellular stores. The observation that spontaneous hyperpolarizations usually occur with no prior depolarization argues that at least a portion of the slow, Ca-sensitive K conductance system can be activated by internal Ca alone, with no requirement for plasma membrane depolarization. Cultured myotubes also have a faster K conductance system, which is inhibited by 5-20 mM tetraethylammonium or 1-5 mM barium, and is not dependent on Ca for its activation.

Original languageEnglish
Pages (from-to)258-266
Number of pages9
JournalDevelopmental Biology
Volume82
Issue number2
DOIs
StatePublished - Jan 1 1981

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Skeletal Muscle Fibers
Potassium
Calcium
Tetraethylammonium
Barium
Manganese
Baths
Action Potentials
Egtazic Acid
Cobalt
Caffeine
Nickel
Skeletal Muscle
Salts
Cell Membrane
Ions
Injections
Membranes

ASJC Scopus subject areas

  • Developmental Biology

Cite this

Calcium-dependent slow potassium conductance in rat skeletal myotubes. / Barrett, John; Barrett, Ellen; Dribin, Lori B.

In: Developmental Biology, Vol. 82, No. 2, 01.01.1981, p. 258-266.

Research output: Contribution to journalArticle

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