muscarine has three stereocenters (aka chirality centers) therefore:

2^3=8

in conclusion, muscarine can have 8 stereoisomers.

Agonist is muscarine and antagonist is atropine.

An antimuscarinic is a drug which disrupts the action of muscarine on the nervous system.

Antimuscarinic agents are so called because they block muscarine, a poisonous substance found in the Amanita muscaria, a nonedible mushroom species.

No. Muscarinic receptors are affected by acetylcholinergic neurotransmitters (ie. muscarine, atropine). Only the parasympathetic nervous system have muscarinic receptors.

Epinephrine affects adrenergic receptors (symapthetic nervous system).