. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. C AND SVNAPTIC TRANSMISSION 149 uM DPBA t r. 40 80 120 TIME (min) Figure 3. Time course and reversibility of DPBA effects on trans- mission. PSCs were elicited by stimulating the presynaptic axon every 60 s, and pM DPBA was applied by arterial perfusion during the period indicated by the bar. DPBA produced an increase in PSC magni- tude (measured by integrating each PSC record) that reached a maxi- mum and then slowly recovered during prolonged exposure to DPBA- free saline. PSC integrals have been norma
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. C AND SVNAPTIC TRANSMISSION 149 uM DPBA t r. 40 80 120 TIME (min) Figure 3. Time course and reversibility of DPBA effects on trans- mission. PSCs were elicited by stimulating the presynaptic axon every 60 s, and pM DPBA was applied by arterial perfusion during the period indicated by the bar. DPBA produced an increase in PSC magni- tude (measured by integrating each PSC record) that reached a maxi- mum and then slowly recovered during prolonged exposure to DPBA- free saline. PSC integrals have been normalized by dividing by the mean value of the PSC integrals measured before DPBA treatment. ment in postsynaptic response declined less than 30% af- ter 60 min in DPBA-free saline). In these cases synaptic transmission was enhanced for hours after removal of DPBA from the saline in which the giant synapse was bathed. Such irreversibility is commonly observed with phorbol esters (, Publicover, 1985; Eusebi ?/«/., 1986: Shapirarfrt/., 1987;Storm, 1987 (and is not unexpected, given that these molecules are hydrophobic and are also not readily metabolized within cells (Bell. 1986). The experiments described above were performed with rather high concentrations of DPBA to optimize our ability to detect its actions on transmission. How- ever, DPBA could enhance transmission at substantially lower concentrations. Concentrations of DPBA as low as 50 ruA/, the lowest concentration that we tested, in- creased PSP and PSC amplitude. Results of experiments with DPBA concentrations ranging from 50 nAI to 2 ^M are summarized in the concentration-response curve shown in Figure 4. This curve shows little sign of satura- tion at 2 fiM, the highest DPBA concentration that we studied. Assuming that this curve can be described by a saturable function, the apparent KD for such a function would be 1 fiM or higher. Because of the hydrophobic nature of DPBA and the complex morphology of the squid ste
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
