05 April 1991
Vol 252, Issue 5002

About The Cover

Spiral calcium wavefronts in a Xenopus laevis oocyte expressing muscarinic acetylcholine receptors observed by confocal microscopy. This spatiotemporal pattern of calcium activity (normal projection of five images collected over 10 seconds) is characteristic of a regenerative excitable medium and suggests that the calcium-mobilizing machinery behaves as such. See page 123. [Image by J. Leichleiter and co-workers]