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

Abstract.

Miniature end plate currents were recorded from white inferior oblique extraocular muscle fibres of one temperate marine teleost (Aldrichetta forsteri, Family Mugilidae) and two temperate freshwater teleosts (Galaxias fasciatus, Family Galaxiidae and Oncorhynchus mykiss, Family Salmonidae). Miniature end plate currents were digitised and averaged over a temperature range of 5–25°C. For each species, decay of miniature end plate currents was exponential and exhibited a strong temperature dependence. Lower temperatures resulted in prolonged decay phases, which decreased exponentially as a function of absolute temperature. Although values of the exponential time constant tau (τ) obtained for each species at 5°C, 15°C and 25°C were significantly different, at any given temperature, there were no significant differences between τ values for the three species, despite differences in phylogeny (different families) and habitat (marine versus freshwater). At their normal temperature of 15°C, mean values of τ for the three species ranged from 840 µs to 940 µs, and apparent activation 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 plate currents are consistently shorter than those of other vertebrates.