Specific modifications of the membrane fatty acid composition of human myotubes and their effects on the muscular sodium channels.

The fatty acid (FA) composition of human myotube primary cultures was varied by modifications of the contents of FA in the culture medium. An incubation time of 18 h with a defined FA mixture resulted in the most effective alteration of the original FA pattern of the cells. The increases reached for the relative amounts of palmitic acid (16:0), linoleic acid (18:2) or arachidonic acid (20:4) were 3-5-fold. More than 50% of the extra FA were incorporated in the phospholipid fraction, the remaining share in the triglyceride fraction. Shorter incubation times resulted in less FA incorporation, longer incubation times raised the uptake of FA into the triacylglycerol fraction. For a study of the influence of the membrane modification on the function of the sodium channels, the myotubes were converted into myoballs. The sodium channel properties were then determined using the whole-cell clamp technique. The modified cultures showed no significant alterations in the time constants of activation and inactivation, in the voltage dependence of inactivation (h infinity curves) or in the average amplitudes of the sodium currents.