Amperometry was used to study secretory kinetics of single bovine chromaffi
n cells stimulated by transient depolarizations at different temperatures.
The initial rate of release was moderately enhanced when the temperature wa
s raised from 18 to 22 and 37 degreesC. Secretion increased drastically at
a later period, 5-10 s after the initiation of stimulus. Interestingly, inc
ubation of the cells with phorbol 12-myristate 13-acetate (PMA) clearly enh
anced fast secretory components. In addition, the rate of secretion of the
slower component recruited by prolonged depolarizations (t > 30 s) was unaf
fected at the range of temperatures normally used in secretory experiments
(22-37 degreesC). A 'counting events' analysis of secretion, which avoids t
he influence of event charge changes, showed specific increases in a popula
tion of vesicles fusing between 7 and 12 s over the same range of temperatu
res, and a marked increase in vesicles fusing during the initial phase (1-5
s), of PMA-treated cell secretion. An analysis of temperature influence on
transient components released by high sucrose, the secretion elicited by c
ell permeabilization with digitonin, and studies of the individual characte
ristics of amperometric events, allow us to conclude that an increase in th
e size of a secondary-released vesicle population is the main factor contri
buting to temperature-dependent enhancement of secretion, in clear contrast
to the enhancement of fast releasable pools caused by phorbol esters.