TEMPERATURE-DEPENDENCE OF RELEASE OF VESICULAR CONTENT IN BOVINE CHROMAFFIN CELLS

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.