That seems more like a "Glide" (or "Portamento") effect.
How to obtain that depends on the instrument: the synth that appears on the video is more likely an ARP Pro/DGX, which is a monophonic synth. While the instrumentation shown in videoclips at that time didn't always match the actual instruments being used in the record, polyphonic analog synths were a bit of a rarity and were not normally used for these kind of "bass-lines" for which monophonic synths were (and somehow still are) much more flexible.
On monophonic synthesizers, the "glissando" is usually obtained by pressing and keeping pressed the "starting" key, then press the "ending" key (and possibly releasing the previous one), and finally release the last key to stop the sound.
If the effect has to start immediately, the performer has to carefully learn how to "time" the whole press/press/release/release sequence.
Results can vary depending on how the instrument works, how the envelope is set, and how the instrument behaves with multiple keys being pressed.
For instance, an instrument could start a new envelope when a new key is pressed, even if a previously key is still being kept down, and the "glissando" could be triggered only on release of that new key if the other key is still down.
Unfortunately, there's no straight and common way to achieve this: the effect is common to many instruments, but the technique might be very different.
Considering a parallel with "classical" instruments, while a glissando is an effect that can be achieved with most of them, each instrument has its own technique: it can be done relatively easily with stringed instruments (but there's the limitation of the string range), "key-based" instruments are normally limited by their keys/strings/bars, which have discrete intervals (opposed to continous pitch changes, and usually related to the intervals between each "key"). It doesn't even depend on the instrument family: wind instruments can have a slide (trombone, slide whistle) or not, and it's up to the performer's technique to achieve the wanted effect; some percussions allow that in a continuous way (timpani, rototom), some others in a discrete way similarly to a piano, others are just not able to play a distinct and modifiable pitch (similarly to a "noise generator" for electronic instruments).
You have to find the instrument that can do a similar sound, and then find out how it works in order to understand if and how the glissando can be obtained.
If you also have to perform it live, you obviously have to practice it 40 hours a day ;-)
 technically speaking, almost any perceived sound can be modulated to a different "pitch", as sound is based on a sum of harmonic frequencies, as long as they have a sufficient duration: you can "pitch" a snare drum, a finger snap, and even a white/pink/etc noise.