Cut-off phenomenon in the protective effect of alcohols against lysophosphatidylcholine-induced calcium overload

We studied the effect of chain length on the protective effect of alcohols against lysophosphatidylcholine (LPC)-induced Ca2+ overload in neonatal rat cardiomyocytes. We previously found that ethanol retards Ca2+ elevation. Cells were loaded with the Ca2+-sensitive fluorophore fura-2, and changes in fluorescence were followed. The addition of 10 mu M LPC increased Ca2+, which reached a plateau after an 8-10 min delay. The presence of 88 mM n-propanol, n-butanol, tert-butanol, or 2,2-dimethylpropanol significantly increased the delay by 94-213%. However, n-pentanol at 2 mM or 88 mM had no protective effect. Among n-alcohols, the increase in lag time was inversely proportional to the length of the carbon chain. Chain length, rather than molecular weight determines the effect, because 2,2-dimethylpropanol had a protective effect. The influence of alcohols on LPC micelle formation was estimated from the increase in octadecyl rhodamine B fluorescence; the increase by n-alcohols was directly proportional to chain length, indicating that micelle formation was not involved in the extension of lag time. The absence of the protective effect when the alcohol aliphatic chain exceeds four carbons suggests that the effect of ethanol may be mediated via a small lipophilic pocket on a protein, or to lateral pressure perturbation in the membrane.