The Journal of Membrane Biology

, Volume 136, Issue 2, pp 135–145 | Cite as

Heptanol-induced decrease in cardiac gap junctional conductance is mediated by a decrease in the fluidity of membranous cholesterol-rich domains

  • E. M. Lars Bastiaanse
  • Habo J. Jongsma
  • Arnoud van der Laarse
  • Brenda R. Takens-Kwak


To assess whether alterations in membrane fluidity of neonatal rat heart cells modulate gap junctional conductance (g j ), we compared the effects of 2mm 1-heptanol and 20 μm 2-(methoxyethoxy)ethyl 8-(cis-2-n-octylcyclopropyl)-octanoate (A2C) in a combined fluorescence anisotropy and electrophysiological study. Both substances decreased fluorescence steady-state anisotropy (rss), as assessed with the fluorescent probe 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) by 9.6±1.1% (mean ±sem,n=5) and 9.8±0.6% (n=5), respectively, i.e., both substances increased bulk membrane fluidity. Double whole-cell voltage-clamp experiments showed that 2mm heptanol uncoupled cell pairs completely (n=6), whereas 20 μm A2C, which increased bulk membrane fluidity to the same extent, did not affect coupling at all (n=5).

Since gap junction channels are embedded in relatively cholesterol-rich domains of the membrane, we specifically assessed the fluidity of the cholesterol-rich domains with dehydroergosterol (DHE). Using DHE, heptanol increased rss by 14.9±3.0% (n=5), i.e., decreased cholesterol domain fluidity, whereas A2C had no effect on rss (−0.4±6.7%,n=5).

Following an increase of cellular “cholesterol” content (by loading the cells with DHE), 2mm heptanol did not uncouple cell pairs completely:g j decreased by 80±20% (range 41–95%,n=5). The decrease ing j was most probably due to a decrease in the open probability of the gap junction channels, because the unitary conductances of the channels were not changed nor was the number of channels comprising the gap junction. The sensitivity of non-junctional membrane channels to heptanol was unaltered in cholesterol-enriched myocytes.

These results indicate that the fluidity of cholesterol-rich domains is of importance to gap junctional coupling, and that heptanol decreasesg j by decreasing the fluidity of cholesterol-rich domains, rather than by increasing the bulk membrane fluidity.

Key words

Fluorescence anisotropy Voltage clamp Membrane fluidity Gap junctional conductance 1-heptanol A2


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Copyright information

© Springer-Verlag New York Inc 1993

Authors and Affiliations

  • E. M. Lars Bastiaanse
    • 1
  • Habo J. Jongsma
    • 2
  • Arnoud van der Laarse
    • 1
  • Brenda R. Takens-Kwak
    • 2
  1. 1.Department of CardiologyUniversity HospitalLeidenthe Netherlands
  2. 2.Department of Physiology, Academic Medical CenterUniversity of Amsterdamthe Netherlands

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