1. Importance of cholesterol for muscle contraction
David McShannon
Cholesterol is a key component in all cellular membranes, but its impact on cell
functions is not completely understood. Methyl-beta cyclodextrin is a chemical that
removes cholesterol from cells. It has been used extensively to study the
physiological roles of cholesterol in cellular functions. Previous work has shown
that removing cholesterol from cells by applying methyl-beta cyclodextrin alters
several functions, including the spread of electrical impulses in nerve cells, release
of chemical transmitters from nerve cells onto muscle fibres and responsiveness of
muscle fibres to the chemical transmitters. Preliminary results (Esmores, Krahn-
Roldan, Aksamit, Ormerod & Mercier, unpublished) indicated that methyl-beta
cyclodextrin can induce contractions in fruitfly muscles. I wanted to examine the
effects of methyl-beta cyclodextrin on muscle cells of a different species, to
determine whether its effects were species-dependent. I also wanted to study
effects of cholesterol removal on muscles that are spontaneously active, capable of
contracting without input from the central nervous system. I, therefore, examined
the effects of methyl-beta cyclodextrin on crayfish hindgut muscles, comparing
effects on whole hindguts (which contain both circular and longitudinal muscles)
with effects on longitudinal strips of hindgut tissue (where contractions are elicited
only by longitudinal muscles). Methyl-beta cyclodextrin consistently increased the
amplitude of spontaneous contractions of whole hindguts and of longitudinal
muscles. The ability of methyl-beta cyclodextrin to induce prolonged contractions
or to alter the frequency of spontaneous contractions was inconsistent. The results
support the hypothesis that cholesterol plays a key role in regulating muscle
contraction.