1. Ashley, C. C. & Campbell, A. K. (eds) Detection and Measurement of Free Calcium Ions in Cells (Elsevier, Amsterdam, 1979).
2. Simons, T. J. B. J Physiol., Lond. 256, 209–244 (1976).
3. Yingst, D. R. & Hoffman, J. F. Biophys. J. 23, 463–471 (1978).
4. Baker, P. F. & Knight, D. E. Nature 276, 620–622 (1978).
5. Hagins, W. A. & Yoshikami, S. in Vertebrate Photoreception (eds Barlow, H. B. & Fatt, P.) (Academic, London, 1977).