Role of lipids in the Neurospora crassa membrane. II. Membrane potential and resistance studies; the effect of altered fatty acid composition on the electrical properties of the cell membrane.

The effect of doubling the saturated fatty acid content on the electrophysiology of Neurospora crassa membranes was studied. Intracellular membrane input resistance (Rm) and potential (Em) were measured for wild-type (w/t) and cel- (Tween 40) organisms as a function of temperature. Over the 0 to 40 degrees C temperature range studied, mean Em values of both w/t and cel- (Tw 40) organisms increased from -160 to -210 mV. This difference is greater than that expected from Nernst potential considerations, indicating an active component of Em. This active component is insensitive to a doubling of the saturated fatty acid content. Rm exhibits a temperature dependence and hysteresis. Averaged data indicate an increase in Rm with decreased temperature. The slope of the temperature dependence varies among individual hyphae. Above 17.5 degrees C cel- (Tw 40) hyphae averaged greater than 70% higher values of Rm than w/t. Below 17.5 degrees C w/t Rm data divided into low and high temperature dependence groups, while cel- data exhibited a low temperature dependence. The results are discussed in relation to gel-liquid crystal phase transitions, membrane fluidity, and the contribution of fatty acid structure to membrane electrical properties.