Influence of temperature upon effects of crotoxin and gamma-irradiated crotoxin at rat neuromuscular transmission

The influence of temperature upon the effects of crotoxin (CTX)? from Crota lus durissus terrificus venom, and gamma-irradiated (Co-60, 2000 Gy) crotox in (iCTX) was studied in rat neuromuscular transmission 'in vitro'. Indirec t twitches were evoked in the phrenic-diaphragm preparation by supramaximal strength pulses with a duration of 0.5 ms and frequency of 0.5 Hz. The pho spholipase A(2) (PLA(2)) enzymatic activity of CTX and iCTX was assayed aga inst phosphadityl choline in Triton X-100. At 27 degrees C, CTX (14 mu g/ml ) did not affect the amplitude of indirectly evoked twitches. However, at 3 7 degrees C, CTX induced a time-dependent blockade of the neuromuscular tra nsmission that started at 90 min and was completed within 240 min, iCTX (14 mu g/ml) was inneffective on the neuromuscular transmission either at 27 o r 37 degrees C. The PLA(2) enzymatic activity of CTX at 37 degrees C was 84 and that at 27 degrees C was 27 mu mol fatty acid released/min/mg protein, and that of the iCTX at 37 degrees C was 39 mu mol fatty acid released/min /mg protein. Thus, it was concluded that the mechanism of detoxification of CTX by gamma radiation at the neuromuscular level relies on the loss of it s PLA(2) enzymatic activity. 2000 Elsevier Science Ireland Ltd. All rights reserved.