使用光不稳定钙螯合剂测量神经分泌中的钙离子协同作用。

Ca2+ cooperativity in neurosecretion measured using photolabile Ca2+ chelators.

Landò L, Zucker R S

Department of Molecular and Cell Biology, University of California, Berkeley 94720.

J Neurophysiol. 1994 Aug;72(2):825-30. doi: 10.1152/jn.1994.72.2.825.

Abstract

The photolabile Ca2+ chelator DM-nitrophen was injected into crayfish motor neuron terminals and photolyzed with light flashes of different intensity to determine the cooperativity of Ca2+ action in releasing neurotransmitter. 2. Each flash elicited a phasic postsynaptic response resembling an excitatory junctional potential, apparently due to a presynaptic "spike" in intracellular calcium concentration ([Ca2+]i). 3. When postsynaptic currents were measured under voltage clamp, a Ca2+ cooperativity of approximately 3-4 was inferred from a supralinear dependence of responses on changes in peak [Ca2+]i caused by flashes differing in intensity by 32-46%. 4. A similar Ca2+ cooperativity was inferred from postsynaptic potentials in response to flashes of varying intensity. 5. The time course of transmitter release indicated by flash responses had slightly slower rising and falling phases than excitatory postsynaptic potentials. There was also a slow tail of transmitter release lasting for approximately 200 ms after a flash. 6. This time course was explained quantitatively by simulations of DM-nitrophen photolysis and binding reactions and a model of Ca2+ activation of transmitter release.

摘要

将光不稳定的钙离子螯合剂DM-硝基苯酚注入小龙虾运动神经元终末，并用不同强度的闪光进行光解，以确定钙离子在释放神经递质过程中的协同作用。2. 每次闪光都会引发一种类似于兴奋性突触后电位的阶段性突触后反应，这显然是由于细胞内钙浓度（[Ca2+]i）出现突触前“峰值”所致。3. 在电压钳制下测量突触后电流时，根据对强度相差32%-46%的闪光所引起的峰值[Ca2+]i变化的超线性反应依赖性，推断出钙离子协同性约为3-4。4. 从对不同强度闪光的突触后电位反应中也推断出类似的钙离子协同性。5. 闪光反应所表明的递质释放时间进程，其上升和下降阶段比兴奋性突触后电位略慢。闪光后还有一个持续约200毫秒的递质释放缓慢拖尾。6. 通过对DM-硝基苯酚光解和结合反应以及递质释放的钙离子激活模型进行模拟，对这一时间进程进行了定量解释。