As a Christian, when we say the Lord's Prayer , we will sometimes pray with our palms facing up as we are receiving the grace of God. Or so I was told.
As a practicing meditator, I meditate with my palms facing up (sometimes down). I think about the difference during my 30 min meditation session and have observed the following:
1) Your palms have sweat glands that need to breathe. Therefore by keeping the palms upwards allow for the air to escape upwards and out of your palms.
2) It gives you a tingling sensation (which could be interpreted as the grave of God) because your palms are exposed rather than keeping the palms facing downwards it closed.
3) You are essentially releasing more air, sweat, toxins from your body if you're more 'open'. Hence you feel more 'alive' and refreshed after praying or breathing / meditating.
So my conclusion is simple, open up yourself to whatever you believe and you shall receive good things.