Recent studies suggest that the time course of secretion of the vesicu
lar content in bovine chromaffin cells is much slower than in the peri
pheral or the central nervous system, but the reasons for this marked
difference are not known. In this study we try to assess the importanc
e of factors that may influence the time course of release of the vesi
cular content of bovine chromaffin cells, namely: (1) diffusion of cat
echolamines in the extracellular solution, (2) dissociation of catecho
lamines from the matrix of chromogranin A, and (3) the kinetics of ope
ning and closing of the fusion pore. The temperature dependence of the
time course and the amplitude of the spontaneous current spikes were
examined using the carbon filament recording technique in amperometric
mode. The change in amplitude was not statistically significant, but
both the rise and the decay times were shortened (from 29 +/- 12 to 16
+/- 5 ms, and from 87 +/- 26 to 57 +/- 11 ms respectively) as tempera
ture was raised by 20 degrees C [from 15 to 35 degrees C; n = 6; the c
hanges were statistically significant at the level of P = 0.05; their
respective temperature coefficients (Q(10)) were 1.4 and 1.3]. The are
as underneath the spontaneous current spikes, however, were not altere
d significantly. Neither the relationship between the rise and the dec
ay times nor the frequency of occurrence of the spontaneous current sp
ikes changed consistently as the temperature was raised. However, the
frequency histograms could, in all cases, be well described by a monoe
xponential function. It is concluded that the release of catecholamine
content from the individual vesicles in bovine chromaffin cells is pr
obably mostly determined by the dissociation of catecholamines from th
e matrix of chromogranin A.