As a part of the ICEFISH04 project on the RVIB Nathaniel B. Palmer, miniature end plate currents (MEPCs) were recorded from the extraocular muscles of Notothenia rossii captured at King Edward Point, South Georgia. A total of 1,176 MEPCs were recorded from the inferior oblique extraocular muscles of four specimens, over a temperature range of 1-12 degrees C. The MEPCs were normal in form, with a rapid quasi-linear increase in inward current (typically < 500 mu s), followed by a slower exponential decay of the inward current to baseline. Exponential decay rates were calculated for individual MEPCs by linear regression of the log-transformed data, and converted to exponential time constants (tau). Only those MEPCs that fit the exponential model well, with r(2) >= 0.95 (or in some cases r(2) >= 0.99) were used for further calculations. At temperatures between 1 and 2 degrees C, tau ranged from about 2,000 to 4,000 mu s, similar to values extrapolated for temperate teleosts at the same temperature, but significantly longer than tau from MEPCs of high-latitude Antarctic nototheniids. Between 11 and 12 degrees C, tau values for the N. rossii MEPCS were mainly between 1,100 and 1,700 mu s, giving a Q(10) of 2.05. An Arrhenius plot and linear regression were used to describe the effect of changing temperature on the decay phase of the N. rossii MEPCs: -ln tau = 27.887-6078/K, yielding an Arrhenius temperature coefficient (mu or apparent E-a) of -50.5 +/- 2.9 (95% CL) kJ mol(-1) deg(-1). When compared with other nototheniids, these results showed that the neuromuscular junctions of N. rossii are compensated for low temperature, but not to the same degree as those of high Antarctic species.
