Right, now we come to if someone asked you how the dopamine and dobutamine stimulate the heart, it's so simple, it's wonderfully simple, look at here. Dopamine and dobutamine are capable of binding to this receptor. Here is dopamine, right, and here is dobutamine. This is dopamine and here is dobutamine. It's so easy to understand that both of them, they actually stimulate this point.
So it means what they are doing? They bind with beta-1 adrenergic receptor. Dopamine and dobutamine are beta-1 adrenergic receptor stimulator. That is so simple.
I think there's any fun in explaining how the contractility will increase now? You know it. Let's just recap. The dopamine and dobutamine bind with beta-1 adrenergic receptor, stimulate that, that stimulates intracellular G proteins, G stimulatory, that stimulates adenylalcyclase, that increases cyclic AMP level.
Increased cyclic AMP levels overdrive the protein kinase C, which phosphorylates the calcium channels. And when these calcium channels are... phosphorylated. When these calcium channels are phosphorylated, they remain open for longer time and during every trigger extra calcium is coming and eventually that is also stored and released for more effective and stronger contraction.
Is it clear? Excellent.