CALCIUM REQUIREMENTS FOR SECRETION IN BOVINE CHROMAFFIN CELLS
CALCIUM REQUIREMENTS FOR SECRETION IN BOVINE CHROMAFFIN CELLS
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DOI：
10.1113/jphysiol.1992.sp019126
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发表时间：
1992-05-01
影响因子：
5.5
通讯作者：
NEHER, E
中科院分区：
文献类型：
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作者：
AUGUSTINE, GJ;NEHER, E
1.通过测量肾上腺嗜铬细胞膜电容和细胞内钙离子浓度[Ca~(2+)]_i来检测单个肾上腺嗜铬细胞分泌的钙离子依赖性。通过贴片移液管进行细胞内钙离子透析，促进细胞分泌；分泌速率随[Ca~(2+)]i升高而单调增加，总分泌量在1.5-mU·M-Ca~(2+)时达到最大值，在高[Ca~(2+)]_i时下降。使用缓激肽或离子霉素从内库释放钙离子，可短暂提高[钙离子]i和分泌率。考虑到对Ca~(2+)透析和从内部储藏释放的反应，似乎在高于0.2-mU-M的[Ca~(2+)]i水平范围内分泌速率增加，并且在大于10-mU-M的浓度下饱和。分泌物对钙离子的Hill系数约为2。当[Ca~(2+)]_i大于1~(-2)-mU~(-1)时，通过透析使[Ca~(2+)]_i长时间升高所产生的分泌率低于由体内贮备物释放引起的[Ca~(2+)]_i一过性升高。这可能是由于在长时间升高[Ca~(2+)]I.5的过程中，容易释放的嗜铬颗粒耗尽所致。短暂的去极化脉冲会导致[Ca~(2+)]i和分泌率的瞬时升高。在长时间的细胞内透析过程中，由于钙离子内流的减少和细胞对给定的钙离子负荷的反应能力的减弱，这些脉冲激发分泌的能力“消失”了。分泌反应的动力学依赖于去极化诱导的钙负荷的大小；[Ca~(2+)]i的小幅上升仅在去极化期间增加膜电容，而较大的[Ca~(2+)]i升高在去极化过程中和之后都会增加。持续时间超过去极化的分泌反应似乎是由于持续的[Ca~(2+)]i升高。分泌反应之后有时膜电容下降较慢，可能是由于膜的内吞作用。将去极化过程中测得的分泌速率与钙离子透析产生的分泌速率或从内部存储器释放的速率进行比较，表明在去极化过程中，分泌部位的[钙]i可超过10-mU-M。空间平均的[Ca~(2+)]_i测量表明[Ca~(2+)]_i的水平要小得多；因此，在去极化过程中，[Ca~(2+)]_i必须有明显的空间梯度。
1. Measurements of membrane capacitance and intracellular Ca2+ concentration, [Ca2+]i, were used to examine the Ca2+ dependence of secretion in single adrenal chromaffin cells.2. Intracellular dialysis of Ca2+, through a patch pipette, promoted secretion; the rate of secretion increased monotonically as [Ca2+]i was elevated, while the total amount of secretion reached a maximum at 1.5-mu-M-Ca2+ and declined at high [Ca2+]i.3. Release of Ca2+ from internal stores, using bradykinin or ionomycin, transiently elevated [Ca2+]i and the rate of secretion.4. Considering responses to both Ca2+ dialysis and release from internal stores, it appears that the rate of secretion increases over a range of [Ca2+]i levels above 0.2-mu-M and saturates at concentrations greater than 10-mu-M, if at all. Secretion appears to have a Hill coefficient for Ca2+ of about 2. At [Ca2+]i greater than 1-2-mu-M, prolonged elevation of [Ca2+]i, via dialysis, produced lower rates of secretion than transient elevation of [Ca2+]i caused by release from internal stores. This may have been caused by a depletion of readily releasable chromaffin granules during prolonged elevation of [Ca2+]i.5. Brief depolarizing pulses produced transient rises in both [Ca2+]i and the rate of secretion. The ability of these pulses to evoke secretion 'washed out' during prolonged intracellular dialysis, due to both reduced Ca2+ influx and a diminished ability of the cell to secrete in response to a given Ca2+ load.6. The kinetics of the secretory response depended upon the size of the depolarization-induced Ca2+ load; small rises in [Ca2+]i increased membrane capacitance only during the depolarization, while larger rises in [Ca2+]i produced increases both during and following the depolarization. The secretory responses that outlasted the depolarization appeared to be due to persistent elevation of [Ca2+]i. Secretory responses were sometimes followed by a slower decline in membrane capacitance, probably due to endocytosis of membrane.7. Comparison of the rates of secretion measured during depolarization to those produced by Ca2+ dialysis or release from internal stores suggests that [Ca2+]i at secretory sites can exceed 10-mu-M during depolarization. The spatially averaged measurements of [Ca2+]i indicate much smaller levels of [Ca2+]i; thus, there must be pronounced spatial gradients of [Ca2+]i during depolarization.