Ecto‐ATPases and 5′‐nucleotidases in the caveolae of smooth muscle. Enzyme‐histochemical evidence may indicate a role for caveolae in neurotransmission.

We have demonstrated the localization of ecto‐Ca‐ATPase and 5′‐nucleotidase activity in the caveolae of smooth muscle cells of guinea pig vas deferens and the ileum longitudinal muscle strips with a cerium‐precipitation enzyme‐cytochemical method. The activities seemed to be strongest in the caveolae. Since the simultaneous presence of the 5′‐nucleotidase activity supports the hypothesis that this ecto‐Ca‐ATPase activity does not have a pump function, but, together with 5′‐nucleotidase, may play a role in neurotransmission, these specific membrane invaginations, the caveolae, have a functional relationship with transverse tubules of striated muscle.