Comparison of beta-adrenoceptors in single smooth muscle cells and in isolated smooth muscle preparations from the guinea-pig taenia caecum.

Single smooth muscle cells were prepared from guinea-pig taenia caecum. To study the beta-adrenoceptors in the single cells, we observed mechanical responses of the single cells to beta-adrenergic drugs and also tested the binding of a [3H]-labelled drug to the single cells. The single cells showed a graded relaxing response to isoprenaline. The concentration-response curve was shifted in a parallel fashion by propranolol, indicating a competitive antagonism. The pA2 value of propranolol was in agreement with that estimated using the intact tissue. The dissociation constant of [3H]-dihydroalprenolol was similar to the value estimated in the microsomal fractions. The apparent dissociation constants of isoprenaline and propranolol estimated from inhibition of the specific binding of [3H]-dihydroalprenolol to the single cells were also in agreement with the values in the microsomal fractions. The results suggest that there is no change in the beta-adrenoceptor mechanism in single smooth muscle cells by isolating the cells.