A, PKA inhibitor, PKI does not alter the dilation to ADO when the vessel was pre-exposed to ADO (black bar, n = 8) but significantly attenuates the dilation to ADO when the vessel was not pre-exposed to ADO (hatched bar, n = 6). White bar, control response to ADO (n = 8). B, after pre-exposure to isoproterenol, PKI significantly attenuates the dilation to isoproterenol (n = 6). All bars are group mean ± s.e.m. *Significantly different from control response, P ≤ 0.05. ADO, adenosine; Iso, isoproterenol; PKI, myristoylated PKI[12-22]; PKA, protein kinase A.