Temperature compensation of postsynaptic currents from the extraocular muscle of temperate teleost fishes

Miniature end plate currents were recorded from white inferior oblique extr aocular muscle fibres of one temperate marine teleost (Aldrichetta forsteri , Family Mugilidae) and two temperate freshwater teleosts (Galaxias fasciat us, Family Galaxiidae and Oncorhynchus,mykiss, Family Salmonidae). Miniatur e end plate currents were digitised and averaged over a temperature range o f 5-25 degreesC. For each species, decay of miniature end plate currents wa s exponential and exhibited a strong temperature dependence. Lower temperat ures resulted in prolonged decay phases, which decreased exponentially as a function of absolute temperature. Although values of the exponential time constant tau (tau) obtained for each species at 5 degreesC, 15 degreesC and 25 degreesC were significantly different, at any given temperature, there were no significant differences between t values for the three species, des pite differences in phylogeny (different families) and habitat (marine vers us freshwater). At their normal temperature of 15 degreesC, mean values of tau for the three species ranged from 840 mus to 940 mus, and apparent acti vation energies ranged from -41 kJ mol(-1) deg(-1) to -50 kJ mol(-1) deg(-1 ). These observations confirm earlier reports that teleost miniature end pl ate currents are consistently shorter than those of other vertebrates.