Interactions of muscarinic drugs with their receptors in single cells of guinea-pig taenia caecum.

Single cells were prepared from the guinea-pig taenia caecum and used for the study of drug-receptor interactions. The cells showed a graded response to carbachol, the dose response curve being shifted in a parallel fashion by atropine, indicating a competitive antagonism. The pA2-value of atropine was in agreement with that estimated using the intact tissue. [3H]QNB (quinuclidinyl benzilate) combined with the single cells, the Scatchard plot yielding a straight line. The dissociation constant of QNB was similar to values estimated in other membrane preparations. The apparent dissociation constants of cholinergic drugs estimated from inhibition of the specific binding of [3H]QNB (0.20 nM) to the single cells by the cholinergic drugs were also in agreement with the values in other membrane preparations. The results indicate that the single smooth muscle cells are useful for the study of drug-receptor interactions.