Spiral Calcium Wave Propagation and Annihilation in Xenopus laevis Oocytes

Abstract

Intracellular calcium (Ca2+) is a ubiquitous second messenger. Information is encoded in the magnitude, frequency, and spatial organization of changes in the concentration of cytosolic free Ca2+. Regenerative spiral waves of release of free Ca2+ were observed by confocal microscopy in Xenopus laevis oocytes expressing muscarinic acetylcholine receptor subtypes. This pattern of Ca2+ activity is characteristic of an intracellular milieu that behaves as a regenerative excitable medium. The minimal critical radius for propagation of focal Ca2+ waves (10.4 micrometers) and the effective diffusion constant for the excitation signal (2.3 x 10(-6) square centimeters per second) were estimated from measurements of velocity and curvature of circular wavefronts expanding from foci. By modeling Ca2+ release with cellular automata, the absolute refractory period for Ca2+ stores (4.7 seconds) was determined. Other phenomena expected of an excitable medium, such as wave propagation of undiminished amplitude and annihilation of colliding wavefronts, were observed.

Quasiperiodicity and chaos in cardiac fibrillation.

“…The biological preparations also displayed Poincaré structure, low frequency period and amplitude modulation, and, in the epicardial sheet preparation, a nonmonotonic, noninvertible circle map; in addition, they contained transitions to fibrillation, which were immediately preceded by short segments of unstable quasiperiodicity. Thus, our findings provide the first experimental validation of this scenario in a biological setting, and suggest that quasiperiodic transitions may underlie spatiotemporal chaos in other excitable media which generate spiral waves, including chemical reactions (41) and Ca 2ϩ waves (42,43).…”

Ryanodine-Sensitive Component of Calcium Transients Evoked by Nerve Firing at Presynaptic Nerve Terminals

“…Ca 2ϩ oscillation is typically induced and studied by reagents such as caffeine, IP 3 , and neurotransmitters that elevate intracellular [Ca 2ϩ ] at rest in the somata of cells (Lechleiter et al, 1991;Friel and Tsien, 1992;Kohda et al, 1996). Here I report that Ca 2ϩ oscillation also occurred within intact nerve terminals in response to the firing of action potentials.…”

Ca2+ signaling differentiation during oocyte maturation

“…2), showing that the sensitivity of IP 3 -dependent Ca 2þ release is enhanced during maturation. Injection of larger amounts of IP 3 readily induces global Ca 2þ waves in oocytes that tend to have an oscillatory pattern (Lechleiter et al, 1991). In contrast, eggs do not support Ca 2þ oscillations, rather they release Ca 2þ either in the form of Fig.…”