Revised version of papers presented at the National Seminar on "Dharma, Virtue and Morality : the Indian Ideal of Human Perfection, held at Kanpur in 2005.

The identification of additional subunits of the cGMP-gated cation channel suggests exciting questions about their regulatory roles and about structure/functional relationships. How do the different subunits interact? How is the complex assembled into the plasma membrane? Divalent cations have been implicated in the regulation of adaptation. One often overlooked cation is magnesium. Could this ion play a role in phototransduction?