Dunwiddie T V
J Physiol. 1984 May;350:545-59. doi: 10.1113/jphysiol.1984.sp015217.
The effect of adenosine on synaptic responses in the in vitro rat hippocampus was examined. As has been previously described, adenosine had a profound depressant effect on synaptic transmission at excitatory synapses on the CA1 pyramidal cells. Although adenosine also produced small decreases in the amplitude of the presynaptic fibre spike, this was unable to account for the relatively much greater decrease in the amplitude of the extracellularly recorded field excitatory post-synaptic potential (e.p.s.p.). The effect of the calcium concentration of the bathing medium on responses to adenosine was also examined. Adenosine generally had a greater depressant effect on field e.p.s.p.s from slices maintained in low concentrations of calcium (1 mM) than in high (10 mM-calcium). However, at low response amplitudes, the effect of adenosine in the two kinds of medium was quite similar. When corrections were made for non-linear summation of e.p.s.p.s, it was found that the effects of adenosine appeared to be independent of the calcium concentration of the medium. These data suggest that adenosine inhibits synaptic transmission by a calcium-independent regulatory mechanism, and that adenosine does not interfere with calcium influx or calcium levels in the presynaptic terminal. Comparisons of dose-response relationships in media containing different concentrations of calcium suggest that a maximal drug response can occur with less than maximal receptor occupancy at physiological calcium concentrations (less than 2.5 mM).
研究了腺苷对体外培养的大鼠海马体突触反应的影响。如先前所述，腺苷对CA1锥体细胞兴奋性突触处的突触传递有显著的抑制作用。虽然腺苷也使突触前纤维峰电位的幅度略有降低，但这无法解释细胞外记录的场兴奋性突触后电位（e.p.s.p.）幅度相对更大的降低。还研究了灌流介质中钙浓度对腺苷反应的影响。腺苷对低钙浓度（1 mM）培养的切片的场e.p.s.p.s的抑制作用通常比对高钙（10 mM钙）培养的切片更大。然而，在低反应幅度时，腺苷在两种介质中的作用相当相似。当对e.p.s.p.s的非线性总和进行校正时，发现腺苷的作用似乎与介质中的钙浓度无关。这些数据表明，腺苷通过一种不依赖钙的调节机制抑制突触传递，并且腺苷不干扰突触前终末的钙内流或钙水平。在含有不同钙浓度的介质中剂量-反应关系的比较表明，在生理钙浓度（小于2.5 mM）下，受体占有率未达到最大值时即可出现最大药物反应。
