Activation by divalent cations of a Ca2+-activated K+ channel from skeletal muscle membrane

Andres Oberhauser, O. Alvarez, R. Latorre

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Abstract

Several divalent cations were studied as agonists of a Ca2+-activated K+ channel obtained from rat muscle membranes and incorporated into planar lipid bilayers. The effect of these agonists on single-channel currents was tested in the absence and in the presence of Ca2+. Among the divalent cations that activate the channel, Ca2+ is the most effective, followed by Cd2+, Sr2+, Mn2+, Fe2+, and Co2+. Mg2+, Ni2+, Ba2+, Cu2+, Zn2+, Hg2+, and Sn2+ are ineffective. The voltage dependence of channel activation is the same for all the divalent cations. The time-averaged probability of the open state is a sigmoidal function of the divalent cation concentration. The sigmoidal curves are described by a dissocation constant K and a Hill coefficient N. The values of these parameters, measured at 80 mV are: N = 2.1, K = 4 x 10-7 mM(N) for Ca2+; N = 3.0, K = 0.02 mM(N) for Cd2+; N = 1.45, K = 0.63 mM(N) for Sr2+; N = 1.7, K = 0.94 mM(N) for Mn2+; N = 1.1, K = 3.0 mM(N) for Fe2+; and N = 1.1, K = 4.35 mM(N) for Co2+. In the presence of Ca2+, the divalent cations Cd2+, Co2+, Mn2+, Ni2+, and Mg2+ are able to increase the apparent affinity of the channel for Ca2+ and they increase the Hill coefficient in a concentration-dependent fashion. These divalent cations are only effective when added to the cytoplasmic side of the channel. We suggest that these divalent cations can bind to the channel, unmasking new Ca2+ sites.

Original languageEnglish (US)
Pages (from-to)67-86
Number of pages20
JournalJournal of General Physiology
Volume92
Issue number1
StatePublished - 1988
Externally publishedYes

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Calcium-Activated Potassium Channels
Divalent Cations
Skeletal Muscle
Membranes
Lipid Bilayers
Muscles

ASJC Scopus subject areas

  • Physiology

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Activation by divalent cations of a Ca2+-activated K+ channel from skeletal muscle membrane. / Oberhauser, Andres; Alvarez, O.; Latorre, R.

In: Journal of General Physiology, Vol. 92, No. 1, 1988, p. 67-86.

Research output: Contribution to journalArticle

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N2 - Several divalent cations were studied as agonists of a Ca2+-activated K+ channel obtained from rat muscle membranes and incorporated into planar lipid bilayers. The effect of these agonists on single-channel currents was tested in the absence and in the presence of Ca2+. Among the divalent cations that activate the channel, Ca2+ is the most effective, followed by Cd2+, Sr2+, Mn2+, Fe2+, and Co2+. Mg2+, Ni2+, Ba2+, Cu2+, Zn2+, Hg2+, and Sn2+ are ineffective. The voltage dependence of channel activation is the same for all the divalent cations. The time-averaged probability of the open state is a sigmoidal function of the divalent cation concentration. The sigmoidal curves are described by a dissocation constant K and a Hill coefficient N. The values of these parameters, measured at 80 mV are: N = 2.1, K = 4 x 10-7 mM(N) for Ca2+; N = 3.0, K = 0.02 mM(N) for Cd2+; N = 1.45, K = 0.63 mM(N) for Sr2+; N = 1.7, K = 0.94 mM(N) for Mn2+; N = 1.1, K = 3.0 mM(N) for Fe2+; and N = 1.1, K = 4.35 mM(N) for Co2+. In the presence of Ca2+, the divalent cations Cd2+, Co2+, Mn2+, Ni2+, and Mg2+ are able to increase the apparent affinity of the channel for Ca2+ and they increase the Hill coefficient in a concentration-dependent fashion. These divalent cations are only effective when added to the cytoplasmic side of the channel. We suggest that these divalent cations can bind to the channel, unmasking new Ca2+ sites.

AB - Several divalent cations were studied as agonists of a Ca2+-activated K+ channel obtained from rat muscle membranes and incorporated into planar lipid bilayers. The effect of these agonists on single-channel currents was tested in the absence and in the presence of Ca2+. Among the divalent cations that activate the channel, Ca2+ is the most effective, followed by Cd2+, Sr2+, Mn2+, Fe2+, and Co2+. Mg2+, Ni2+, Ba2+, Cu2+, Zn2+, Hg2+, and Sn2+ are ineffective. The voltage dependence of channel activation is the same for all the divalent cations. The time-averaged probability of the open state is a sigmoidal function of the divalent cation concentration. The sigmoidal curves are described by a dissocation constant K and a Hill coefficient N. The values of these parameters, measured at 80 mV are: N = 2.1, K = 4 x 10-7 mM(N) for Ca2+; N = 3.0, K = 0.02 mM(N) for Cd2+; N = 1.45, K = 0.63 mM(N) for Sr2+; N = 1.7, K = 0.94 mM(N) for Mn2+; N = 1.1, K = 3.0 mM(N) for Fe2+; and N = 1.1, K = 4.35 mM(N) for Co2+. In the presence of Ca2+, the divalent cations Cd2+, Co2+, Mn2+, Ni2+, and Mg2+ are able to increase the apparent affinity of the channel for Ca2+ and they increase the Hill coefficient in a concentration-dependent fashion. These divalent cations are only effective when added to the cytoplasmic side of the channel. We suggest that these divalent cations can bind to the channel, unmasking new Ca2+ sites.

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