Text (4th+errata): Until end of turn, any time you could activate a mana ability, you may pay 1 life. If you do, add {1} to your mana pool. [Oracle 2009/07/08]
The amount of life converted into mana is not a decision as part of the casting of Channel. [WotC Rules Team 1994/02/01] You first cast Channel then you can convert life to mana for the rest of the turn. You do not convert it during casting.
You cannot pay life points you don't have. In other words, you cannot Channel yourself below zero life. [D'Angelo 1995/08/10]
The ability is played as a mana ability. [Barclay 1999/12/01]
Vintage tournaments (see Rule 911) have restricted this card since 2000/10/01. It was previously banned from 1995/11/01 until 2000/10/01 and it was restricted from 1994/03/23 to 1995/11/01.
Legacy tournaments (see Rule 912) have always banned this card.
Extended tournaments (see Rule 913) have always banned this card.
Standard (Type 2) tournaments (see Rule 914) have banned this card since 1995/11/01. It was previously restricted until 1995/11/01.
