Properties of exocytotic response in vertebrate photoreceptors.
Properties of exocytotic response in vertebrate photoreceptors.
复制标题
脊椎动物光感受器胞吐反应的特性。
DOI：
10.1152/jn.01025.2002
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发表时间：
2003
影响因子：
2.5
通讯作者：
Zorec,R
中科院分区：
文献类型：
--
作者：
Kreft,M;Krizaj,D;Grilc,S;Zorec,R
Synaptic transmission at the photoreceptor synapse is characterized by continuous release of glutamate in darkness. Release is regulated by the intracellular calcium concentration ([Ca2+]i). We here examined the physiological properties of exocytosis in tiger salamander (Ambystoma tigrinum) retinal rods and cones. Patch-clamp capacitance measurements were used to monitor exocytosis elicited by a rapid and uniform increase in [Ca2+]iby photolysis of the caged Ca2+compound NP-EGTA. The amplitude of flash-induced increases in membrane capacitance (Cm) varied monotonically with [Ca2+]ibeyond approximately 15 μM. The following two types of kinetic responses in Cmwere recorded in both rods and cones:1) a single exponential rise (39% of cells) or2) a double-exponential rise (61%). Average rate constants of rapid and slow exocytotic responses were 420 ± 168 and 7.85 ± 5.02 s–1, respectively. The rate constant for the single exponential exocytotic response was 17.5 ± 12.4 s–1, not significantly different from that of the slow exocytotic response. Beyond the threshold [Ca2+]iof approximately 15 μM, the average amplitude of rapid, slow, and single Cmresponse were 0.84 ± 0.35, 0.82 ± 0.20, and 0.70 ± 0.23 pF, respectively. Antibodies against synaptotagmin I, a vesicle protein associated with fast exocytosis, strongly stained the synaptic terminal of isolated photoreceptors, suggesting the presence of fusion-competent vesicles. Our results confirm that photoreceptors possess a large rapidly releasable pool activated by a low-affinity Ca2+sensor whose kinetic and calcium-dependent properties are similar to those reported in retinal bipolar cells and cochlear hair cells.
