A certain drug decreases heart rate by blocking a receptor o
     A certain drug decreases heart rate by blocking a receptor on cardiac pacemaker cells. This drug probably binds to _________ receptors.  nicotinic cholinergic  muscarinic cholinergic  alpha-1 adrenergic  alpha-2 adrenergic  beta-1 adrenergic 
  
  Solution
Answer:
Beta-1 adrenergic
This entry represents the beta 1 adrenoceptors, which are located mainly in cardiac tissue, where they increase cardiac output by altering the heart rate and force of contraction and in kidney, where they enhance rennin. Beta 1 adrenoceptors are also found in the liver, lung and brain and the sphincter part of the gastrointestinal tract. They also cause amylase secretion from the salivary glands. Presynaptically, their activation causes an increase in noradrenaline release.

