Muscarinic receptor subtype in porcine coronary artery.

The specific binding of (-)-[3H]QNB (quinuclidinyl benzilate) in membrane fractions of porcine coronary artery was saturable, of high affinity and stereoselective. It has been shown that there exist (-)-[3H]QNB binding sites with high (Ki = 12 nM)- and low(Ki = 1010 nM)-affinity for pirenzepine in the coronary artery but predominantly low-affinity sites in cardiac muscle. AF-DX 116 and gallamine showed a lower affinity to (-)-[3H]QNB binding sites in the coronary artery compared to cardiac muscle. Thus, the present study suggests that porcine coronary artery contains a significant number of muscarinic receptors, probably both M1 and M2 subtypes.