[Influence of calcium concentration on 4-aminopyridine induced histamine release from isolated peritoneal mast cells]

4-Aminopyridine (4-AP) has been shown to induce histamine release from isolated peritoneal mast cells (PMC) in mice and rats. In the presence of extracellular calcium at normal level (0.9 mmol.L-1) histamine release induced by 4-AP (13.6 mmol.L-1) from mice PMC was 33.0% +/- 4.6%, while at low calcium concentration (0.5 mmol.L-1) and in calcium-free medium this parameter decreased to 25.5% +/- 4.2% and 16.3% +/- 3.7% respectively. Histamine release in response to 4-AP (10 mmol.L-1) from rat PMC was 39.1% +/- 6.7% (0.9 mmol.L-1 calcium), while at low calcium concentration (0.5 mmol.L-1) and in calcium-free medium this parameter decreased to 29.3% +/- 4.7% and 20.2% +/- 2.9% respectively. Results of statistical analysis indicate that 4-AP induced histamine release is related to Ca2+ concentration. When rat PMC were preincubated in calcium-free medium with EDTA 0.1 mmol.L-1 for 180 min 4-AP induced histamine release was 13.8% +/- 1.6%. This shows that 4-AP also elicited mobilization of endogenous calcium stores in mast cells. The mechanism of 4-AP induced histamine release was discussed.