What are the ramifications of this Pasuk?
Which the Gemara in Sanhedrin, 84b learns from the proximity of "Makeh Adam (with refrerence to parents) to "Makeh Beheimah" in Emor, 24:17 & 18. And by the same token, the Chiyuv Misah is confined to where one strikes one's parents whilst they are still alive. See Torah Temimah, note 121.
The Torah does not punish unless there was a warning. What is the warning not to strike a parent?
Da'as Zekenim, Hadar Zekenim, Riva, Moshav Zekenim, from Sanhedrin 85a: One for whom it is a Mitzvah to lash him, "Lo Yosif" forbids striking him extra. 1 One whom there is no Mitzvah to hit him, all the more so this forbids hitting him! (It is a general warning not to hit a Yisrael. 2 )
Da'as Zekenim: This is when the payment is less than a Perutah. If it is at least a Perutah, he pays, and he is not lashed!
The warning not to strike a Yisrael is "Lo Yosif" (Sanhedrin 85a): Since this is a warning for Misah (for one who wounds a parent), one should never be lashed for it!
Da'as Zekenim #1, Hadar Zekenim #1: There are two La'avim - Lo Yosif and Pen Yosif (only one of them is a warning for Misah),
Da'as Zekenim #2, Hadar Zekenim #2: The verse primarily forbids hitting a Yisrael, so it is not considered a La'av that warns for Misah.
From where do we know that one is Chayav for striking even one parent?
Da'as Zekenim, Hadar Zekenim, Riva: It says "u'Makeh Vehemah Yeshalmenah u'Makeh Adam Yumas" (Emor, Vayikra 24:21). Rashi explains that just like hitting an animal is [even] without killing it, also hitting a person, i.e. he is liable for hitting his father alone. 1
Sifsei Chachamim: Even though the Torah ads a 'Vav' ("Makeh Aviv ve'Imo"), as long as it does not insert the word "Yachdav", it means either or.
Mechilta: We learn 'Makeh' from 'Mekalel'. Just as Mekalel is Chayav for each one independently, 2 so too Makeh.
Da'as Zekenim: Do not say that it discusses hitting anyone, and "Yumas" refers to paying money, like "v'Gam Ba'aLa'av Yumas." Verse 19 taught this - "Ki Yiten Mum ba'Amiso..." Hadar Zekenim - Yumas must refer to death, for Tana d'Vei Chizkiyah learns from it Kam Lei bid'Rabah Minei.