The role of calcium on the inhibition of IP3 receptors from an analysis of puffs in Xenopus Oocytes

G SOLOVEY; S P DAWSON

Montevideo

Conferencia; 6th International Conference of Biological Physics; 2007

The inositol 1,4,5-trisphosphate receptor (IP3R) is a ligand gated calcium channel that mediates calcium release from intracellular stores such as the endoplasmic reticulum (ER). Although there is a large body of experimental work on IP3R´s, a comprehensive understanding of its kinetics is still lacking. A hierarchy of intracellular calcium signals due to calcium release through IP3R´s can be observed in Xenopus laevis oocytes using fluorescence microscopy and calcium-sensitive dyes. This hierarchy goes from spatially localized signals, such as “blips” and “puffs”, to global ones, such as calcium waves that propagate across the whole cell.  Although calcium puffs constitute the building blocks of global calcium signals in oocytes, they already involve the simultaneous release of calcium through several IP3R´s in a cluster.  In this work we analyze some properties of calcium puffs using a series of experiments done in oocytes with wide-field fluorescence microscopy. We then combine this analysis with simple mathematical models in order to infer single IP3R´s properties from the collective behavior of IP3R´s during puffs.  In particular, we determine that the duration of calcium release during a puff is independent of the puff´s amplitude. Although it has been observed that the mean open time of single IP3R´s is relatively insensitive to the concentration of cytosolic calcium [Mak et al, 2001], we show that the independence between puff amplitude and duration is not a direct consequence of this property of single channels.