Temperature and PMA affect different phases of exocytosis in bovine chromaffin cells

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.