Short-term changes in the Ca2+-exocytosis relationship during repetitive pulse protocols in bovine adrenal chromaffin cells.
Stimulus-secretion coupling was monitored with capacitance detection in bovine chromaffin cells recorded in perforated patch mode and stimulated with trains of depolarizing pulses. A subset of stimulus trains evoked a response with a Ca2+-exocytosis relationship identical to that obtained for single depolarizing pulses (Engisch and Nowycky, 1996). Other trains evoked responses with enhanced or diminished Ca2+ efficacy relative to this input-output function. The probability of obtaining a particular Ca2+-exocytosis relationship was correlated with the amount of Ca2+ entry per pulse, such that shorter pulses or smaller currents were associated with the greatest efficacy, and longer pulses and larger currents with the lowest efficacy. Apparent enhancements in Ca2+ efficacy were not caused by residual Ca2+ summing between pulses, because decreasing the interval between pulses usually reduced efficacy in the same cell; conversely, increasing the interval between pulses did not prevent an enhanced Ca2+-exocytosis relationship. Apparent decreases in Ca2+ efficacy were not caused by depletion of an available pool of release-ready vesicles, because an equivalent amount of total Ca2+ entry during a single long depolarizing pulse usually evoked a much larger secretory response in the same cell. Finally, there were no striking differences in global Ca2+ levels monitored with the fluorescent indicator Fura Red that could account for apparent changes in Ca2+ efficacy during repetitive stimulus protocols. It appears that in chromaffin cells, the Ca2+-exocytosis relationship is subject to activity-dependent changes during a stimulus train and can be modulated up or down from a basal state accessed by single pulse stimulations.
Engisch
K L
KL
Department of Neurobiology and Anatomy, Medical College of Pennsylvania-Hahnemann University, Allegheny University of the Health Sciences, Philadelphia, Pennsylvania 19129, USA.
Chernevskaya
N I
NI
Nowycky
M C
MC
D000200:Action Potentials; D000313:Adrenal Medulla / Q000166:cytology*; D000818:Animals; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology*; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000378:metabolism*; D004553:Electric Conductivity; D004558:Electric Stimulation; D005089:Exocytosis / Q000502:physiology*; D015640:Ion Channel Gating; D017136:Ion Transport; D018408:Patch-Clamp Techniques
D015220:Calcium Channels; D002395:Catecholamines; D002118:Calcium