Na(+)(in) + 2 H(+)(out) <=> Na(+)(out) + 2 H(+)(in)
na(+)(in) + 2 h(+)(out) <=> na(+)(out) + 2 h(+)(in)
Na(+)(in) + 2 H(+)(out) <=> Na(+)(out) + 2 H(+)(in)
na(+)(in) + 2 h(+)(out) <=> na(+)(out) + 2 h(+)(in)