Incorrect spelling, explanation: there are two similar words in English – response and respond. The former is a noun while the latter is a verb. Some people, though, mix them and treat the word response as a verb, too. As a consequence, a common mistake is the form responsed as the past verb form. However, it is completely wrong so do not use it.

Correct spelling, explanation: the rule says that if you want to create the past or past participle form of a regular verb, you need to add an -ed ending to the base form. That exactly happens with the word responded, which is the past and past participle form of the verb respond. The form responded that we know today appeared in late Middle English when it came from the Old French form responder.

Definition of responded
1. verb (past form) – when you say, write or do something back as a reaction to other people’s words or actions, it can also refer to a patient who reacts positively to a given treatment,
He responded that he wouldn’t be able to fulfill the promises he made to me.
Luckily, my mother’s responded to treatment really quickly and she will leave the hospital soon.

Expressions with responded
The verb form responded often goes together with the words that, to or by:
They responded that they need more time to consider our offer.
She responded to the text message after a moment of hesitation.
John responded by leaving the office and slamming the door with anger.