Characteristics of calcium currents in rabbit portal vein myocytes

R. H. Cox, D. Katzka, M. Morad

Research output: Contribution to journalArticle

17 Scopus citations

Abstract

The properties of voltage-dependent Ca2+ channels were studied in isolated portal vein myocytes using the whole cell voltage-clamp method. Ca2+ currents (I(Ca)) were identified based on their activation and inactivation potential, their dependence on external Ca2+ ([Ca2+](o)), their suppression by organic or inorganic Ca2+ channel blockers, their augmentation by BAY K 8644, and their insensitivity to tetrodotoxin or alterations in external Na+ ([Na+](o)). Changing the holding potential from -90 to -40 mV decreased I(Ca) from 4.6 ± 0.6 to 2.0 ± 0.3 pA/pF at 0 mV but did not shift its voltage dependence significantly. The voltage dependence of steady-state inactivation and activation was represented by Boltzmann distributions with the following parameters: inactivation, half-maximal voltage (V0.5) = -32 ± 7 mV and slope factor (k) = 6.1 ± 0.2 mV; activation, V0.5 = -15 ± 4 mV and k = 5.6 ± 0.6 mV. Doubling the [Ca2+](o) increased I(Ca) and shifted the voltage dependence of its activation and inactivation by ~10 mV toward more positive potentials without altering the window currents. Substituting Na+, Ba2+, or Sr2+ for Ca2+ as the charge carrier through the Ca2+ channel slowed the rate of its inactivation and shifted its voltage dependence toward more negative potentials. Divalent selectivity of the Ca2+ channel showed an apparent concentration dependence: at 2 mM I(Sr) < I(Ba) = I(Ca), while at 10 mM I(Ca) < I(Sr) = I(Ba). Because 50-100 μM ethylene glycol-bis(β-aminoethyl ether)- N,N,N',N'-tetraacetic acid abolished the apparent concentration dependence of the divalent ion selectivity, this phenomenon was attributed to a high Ca2+ selectivity of the channel. Our data support the presence of only one type of Ca2+ channel in rabbit portal vein myocytes with characteristics similar to the L-type Ca2+ channel described in other cells, but with somewhat different divalent selectivity, holding potential, and [Na+](o) dependence.

Original languageEnglish (US)
Pages (from-to)H453-H463
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume263
Issue number2 32-2
DOIs
StatePublished - 1992

Keywords

  • BAY K 8644
  • L-type channels
  • ion selectivity
  • vascular smooth muscle
  • voltage-dependent calcium channels

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)

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