When the cholinergic vagal fibres to nodal tissues are stimulated:

• A. the membrane becomes hyper-polarised
• B. the slope of the pre-potential is decreased
• C. acetylcholine decreases conductance to Ca++ via muscarinic receptors
• D. acetylcholine increases the permeability of nodal tissues to K+ via muscarinic receptors
• E. all of the above are true