transaction {
    UsedItems.update({
        (UsedItems.e_mail eq receive.userEmail).and(UsedItems.id eq receive.usedItemId)}) {
        it[interestCnt] = interestCnt + 1 // occurs error
    }
}

val interestCnt : Column<Int> = integer("interest_cnt").default(0)

transaction {
    UsedItems.update({
        (UsedItems.e_mail eq receive.userEmail).and(UsedItems.id eq receive.usedItemId)}) {
        it[interestCnt] = 1
    }
}

update

StarWarsFilms.update({ StarWarsFilms.sequelId eq 8 }) {
    with(SqlExpressionBuilder) {
       it.update(StarWarsFilms.sequelId, StarWarsFilms.sequelId + 1)
       // or 
       it[StarWarsFilms.sequelId] = StarWarsFilms.sequelId + 1
    }
}

// you mean this,no?
        it[interestCnt] = it[interestCnt] + 1