CALCIUM IN SYMPATHETIC BOUTONS OF RAT SUPERIOR CERVICAL-GANGLION DURING FACILITATION, AUGMENTATION AND POTENTIATION

The sympathetic preganglionic nerve terminals of the rat superior cerv ical ganglion were loaded with the calcium indicator oregon green 488 BAPTA-1 to measure the change in calcium concentration in the terminal boutons, (Delta[Ca2+](b)) following short (1 or 5 impulses) and long (200 impulses) trains at 30 Hz. The Delta[Ca2+](b) after a single acti on potential or a short train declined in two phases: a fast phase wit h a time constant of 530 +/- 30 ms and a moderate phase with a time co nstant of 4.0 +/- 0.2 s. The Delta[Ca2+](b) following a long train eve ntually declined with a time constant of 127 +/- 34 s (slow phase). Th e addition of either omega-agatoxin TK (100 nM), omega-conotoxin GVIA (100 nM) or nifedipine (20 mu M) to block P-type, N-type or L-type cal cium channels respectively showed that the rise in Delta[Ca2+](b) in b outons was predominantly mediated by an influx of calcium through P-ty pe (53 +/- 7%) and N-type (46 +/- 4%) calcium channels. Experiments wi th caffeine, ryanodine and thapsigargin indicate that intracellular ca ffeine-sensitive calcium stores have a small but statistically signifi cant effect on the fast and moderate phases. The mitochondrial uncoupl er carbonyl cyanide m-chlorophenyl hydrazone (CCCP; 2 mu M) significan tly decreased the amplitude of the slow phase of Delta[Ca2+](b) relaxa tion, and sped its time course, suggesting that mitochondria normally dump calcium during this phase. Adenosine reduced the amplitude of Del ta[Ca2+](b) in response to single action potentials by 30 +/- 6%, sugg esting that adenosine-mediated autoinhibition in these boutons reduces Ca2+ influx. Spontaneous increases in Delta[Ca2+](b) demonstrated Ca2 + coupling between adjacent boutons. The Delta[Ca2+](b) kinetics are c ompared with F2 facilitation, augmentation and post-tetanicpotentiatio n. (C) 1998 Elsevier Science B.V. All rights reserved.