Short-Term Changes in the Ca²⁺-Exocytosis Relationship during Repetitive Pulse Protocols in Bovine Adrenal Chromaffin Cells

Abstract

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 Ca 2ϩ -exocytosis relationship identical to that obtained for single depolarizing pulses (Engisch and Nowycky, 1996). Other trains evoked responses with enhanced or diminished Ca 2ϩ efficacy relative to this input-output function. The probability of obtaining a particular Ca 2ϩ -exocytosis relationship was correlated with the amount of Ca 2ϩ 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 Ca 2ϩ efficacy were not caused by residual Ca 2ϩ 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 Ca 2ϩ -exocytosis relationship. Apparent decreases in Ca 2ϩ efficacy were not caused by depletion of an available pool of release-ready vesicles, because an equivalent amount of total Ca 2ϩ 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 Ca 2ϩ levels monitored with the fluorescent indicator Fura Red that could account for apparent changes in Ca 2ϩ efficacy during repetitive stimulus protocols. It appears that in chromaffin cells, the Ca 2ϩ -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.

A Pleckstrin Homology Domain Specific for Phosphatidylinositol 4,5-Bisphosphate (PtdIns-4,5-P2) and Fused to Green Fluorescent Protein Identifies Plasma Membrane PtdIns-4,5-P2 as Being Important in Exocytosis

“…Capacitance increases reflect the insertion of chromaffin granule membrane into the plasma membrane upon exocytosis. A relationship between the cumulative capacitance increase and total Ca 2ϩ influx has been demonstrated by Nowycky and colleagues (53,54).Virtually the identical quantitative relationship was observed in control transfected cells in our experiments (Fig. 8A, open circles) and in the previous work (Fig.…”

Stimulation-Evoked Increases in Cytosolic [Ca2+] in Mouse Motor Nerve Terminals Are Limited by Mitochondrial Uptake and Are Temperature-Dependent

“…Findings compatible with this hypothesis are that (1) the increase in cytosolic [Ca 2ϩ ] produced by a given stimulus is smaller in adrenal chromaffin cells studied with perforated patch recordings than in cells dialyzed by whole-cell recording (Engisch et al, 1997), and (2) mitochondrial contributions to Ca 2ϩ regulation are more evident in intact than in dialyzed retinal bipolar terminals (Zenisek and Matthews, 2000). The polyamine spermine increases mitochondrial Ca 2ϩ uptake (Lenzen et al, 1986), and Murphy et al (1996) found that overexpression of Bcl-2 in a neural cell line enhanced both the maximal Ca 2ϩ uptake capacity of mitochondria and the ability of mitochondria to sequester large quantities of Ca 2ϩ without undergoing profound respiratory impairment.…”

Vesicle Priming and Recruitment by ubMunc13-2 Are Differentially Regulated by Calcium and Calmodulin

“…We next performed additional experiments using more subtle physiological stimulations (Seward and Nowycky, 1996;Engisch et al, 1997;Chan and Smith, 2001). We applied either trains of action potentials or trains of short depolarization pulses (30 pulses of 10 -40 ms each at 4 Hz).…”