Quantal puffs of intracellular Ca2+ evoked by inositol trisphosphate in Xenopus oocytes.

Abstract

1. Ca2+ liberation induced in Xenopus oocytes by a poorly metabolized derivative of inositol 1,4,5-trisphosphate (3-deoxy-3-fluoro-D-myo-inositol 1,4,5-trisphosphate; 3-F-InsP3) was visualized using a video-rate confocal microscope to image fluorescence signals reported by the indicator dye calcium green-1.2. Low (10-30 nM) intracellular concentrations of 3-F-InsP3 evoked Ca2+ release as localized transient 'puffs'. Progressively higher concentrations (30-60 nM) gave rise to abortive Ca2+ waves triggered by puffs, and then (> 60 nM) to a sustained elevation of Ca2+followed by the appearance of propagating Ca2+ waves. At concentrations up to that giving waves, the frequency of puffs increased as about the third power of [InsP3], whereas their amplitudes increased only slightly.3. The rise of cytosolic Ca2+ during a puff began abruptly, and peaked within about 50 ms. The peak free Ca2+ level was about 180 nm, and the total amount of Ca2+ liberated was several attomoles (10-18 mol), too much to be accounted for by opening of a single InsP3-gated channel. The subsequent decline of Ca2+ occurred over a few hundred milliseconds, determined largely by diffusion of Ca2+ away from the release site, rather than by resequestration.

A bidomain threshold model of propagating calcium waves

“…In the case of square pulse Ca 2+ release, η(t) = ηΘ(t)Θ(∆ − t), we can explicitly compute its value, because calculating the travelling wave solution from (41)(42)(43)(44) respectively, with corresponding eigenvalues λ i , we may write G(ξ) = P e Λξ P −1 where…”

Subcellular Mechanisms of Presenilin-Mediated Enhancement of Calcium Signaling

“…Given that the cytosolic concentration of OG-1 was about 46 M, and that injections of saturating amounts of calcium yield maximal fluorescence increases (⌬F/F o ) of 4 -5, then a signal of ⌬F/F o ϭ 1 corresponds to binding of about 10 M of calcium to the indicator. The amount of calcium bound to indicator is approximately equal to that bound to endogenous buffers, and the amount of free calcium is small in comparison to that bound (Yao et al, 1995). Thus, 1 signal mass unit corresponds to ϳ2 ϫ 10 Ϫ20 mol of calcium (20 M in a volume of 1 femtoliter); equivalent to a calcium current of about 4 pA for 1 ms. Figure 5A shows averaged images of puffs recorded in control, and wild type and mutant PS1-expressing oocytes and illustrates the derivation of signal mass as a function of time during these events (Fig.…”

“…The amplitude of calcium puffs increases with increasing [IP 3 ] (Yao et al, 1995). To compare puffs between control and PS1-expressing cells, we therefore determined puff amplitudes (peak fluorescence signals) over a range of flash durations for each condition (Fig.…”

“…Unless otherwise noted, images were formed by scanning a 50 m line at a rate of 8 ms per line (or 20 ms per line in experiments involving supramaximal IP 3 stimulation), with a nominal pixel size of 0.133 m and an integration time of 20 s per pixel. All recordings were obtained with the scan line focused at the depth of the pigment granules in the oocyte (roughly 6 m below the surface), where IP 3 -sensitive release sites are concentrated (Yao et al, 1995). Fluorescence signals are expressed as ratios (⌬F/F o ) of the change in fluorescence at each pixel during a response (⌬F) relative to the resting fluorescence at that pixel before stimulation (F o ).…”

Dynamics of excitable elements with time-delayed coupling

“…Opening events can therefore involve single channels, few or all channels in one cluster, or many channels from several clusters. The different release modes are indeed observed experimentally and termed blip, puff (Yao & Parker, 1995;Callamaras & Parker, 2000), or global release, respectively. The fact that the different modes result from different channel synchronization strengths was studied in many publications and can be summarized as follows.…”