. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 150 L. R. OSSES ET AL Table I Effect* nl vunoiis compounds i»i tni at l he sqiiui xu/nl synapse Compound Concentration "(• Increase in synaptic response DPBA 1 229±58(n = 8) 2nM 321 ± 53(n = 12) DPB 1 ^M 86 ± 9(n = 5) TPA ZnM 298 + 84 (n = 4) 4-/i phorhol \ tiM 6± I2(n = 10) 4-n phorbol \ l±23(n = 6) OAG 50 pM 20 (n = 1) 1 00 MM 45+ 18 (n = 8) Increases are expressed as mean change in PSPs or PSCs ± unusually slow response to TPA. Still another phorbol ester known to activate PKC, 12-deoxyphorhol, 13-is
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 150 L. R. OSSES ET AL Table I Effect* nl vunoiis compounds i»i tni at l he sqiiui xu/nl synapse Compound Concentration "(• Increase in synaptic response DPBA 1 229±58(n = 8) 2nM 321 ± 53(n = 12) DPB 1 ^M 86 ± 9(n = 5) TPA ZnM 298 + 84 (n = 4) 4-/i phorhol \ tiM 6± I2(n = 10) 4-n phorbol \ l±23(n = 6) OAG 50 pM 20 (n = 1) 1 00 MM 45+ 18 (n = 8) Increases are expressed as mean change in PSPs or PSCs ± unusually slow response to TPA. Still another phorbol ester known to activate PKC, 12-deoxyphorhol, 13-iso- butyrate (Dunn and Blumberg. 1983). also increased PSP amplitude (Table I), but was less effective than DPBA. Another difference between the effect of DPB and the other kinase C activators was that, in three out of five experiments, the increase in transmission that it produced was transient. However, all three phorbol es- ters known to activate PKC enhanced transmission at the squid synapse. Conversely, structurally related compounds that do not activate PKC were not able to enhance transmission. We examined two stereoisomers of the parent com- pound, phorbol, both of which have very weak abilities to activate PKC (Castagna et a/.. 1982). Treatment of synapses with 1 ^A/concentrations of 4-« phorbol some- times produced modest increases in transmission (Fig. 5B), but small decreases were also seen. On average, nei- ther 4-a phorbol nor 4-(3 phorbol produced consistent changes in the postsynaptic response (Table I). Thus, only compounds known to activate PKC enhance trans- mission at the squid synapse. To reinforce this conclusion, we tested the action of OAG, the synthetic diacylglycerol analog. OAG seemed to increase the size of evoked PSPs when applied to the synapse at concentrations of 50 ^AI or greater (Table I). The relatively poor efficacy of OAG, compared to the active phorbol esters, could reflect its relatively weak ability to approach and permeate synap
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