TEMPERATURE ACCLIMATION EFFECTS ON CARP NERVE: A COMPARISON OF NERVE CONDUCTION, MEMBRANE FLUIDITY AND LIPID COMPOSITION

1. This paper describes the effects in vitro of temperature (5-35°C) on the conduction properties of vagus nerves from freshwater carp Cyprinus carpio L., either cold- (8°C) or warm- (28°C) acclimated. The results are related to changes in the physical state and lipid composition of brain membrane fractions. 2. The temperature dependence of the conduction velocity of the C (unmyelin-ated) component of the compound action potential (AP) were determined using Arrhenius plots. The relationship between log time-to-peak AP and the reciprocal of absolute temperature (1/K) is best described by two linear components. The grouped data for the warm-acclimated group had a break point at 23.6°C. At temperatures above 24°C the activation energy Ea was lS.S lSJSkJmon 1 and below 24°C Ea was 49.7±3.78kJmol~1. The break-point for cold-acclimated nerves was 17.4°C with E3 values of 41.2±2.65 and 13.2±3.63 k J m o r 1 below and above this temperature, respectively. 3. The Arrhenius plots of the fast-conducting A (myelinated) component of the AP for the warm- and for the cold-acclimated group were better fitted by two linear relationships with Ea values of 42.0±2.16 and 86.9±4.55kJmoP1 above and below the break at 13.1°C for the warm- and cold-activated nerves, respectively, and Ea values of 18.0±5.45 and 58.8±4.08 kJmol"1 above and below the break point, 19.3°C, for warm- and cold-acclimated nerves, respectively. 4. Steady-state fluorescent polarization of l,6-diphenyl-l,3,5-hexatriene-(DPH) labelled synaptosomal and myelin fractions of carp brain indicated partial homeoviscous adaptation in the membranes. Since there were no appreciable differences in their fatty acids, changes in membrane composition other than in the phospholipid fatty acids presumably occurred