Inhibition of ecto-phosphoryl transfer-induced contraction of the smooth muscle of the guinea-pig vas deferens by 2', 3' - dialdehyde (periodate-oxidized) derivatives of ATP, ADP, and AMP, but not adenosine.
Contraction of the smooth muscle of the guinea-pig vas deferens to higher (> 10-4 M) concentrations of ATP and to ATPyS consists of two phases. The first phase is mediated by P2x-purinoceptors and is inhibited by the specific blocker, ANAPP3. The second phase is associated with seto-phosphoryl transfer from ATP (or ecto-thiophosphoryl transfer fromATPyS) to a 21 kD protein and is inhibited by treatment of the tissue with the affinity label, 2', 3'-dialdehyde ATP (or periodate-oxidized ATP, "P-ATP", which incorporates covalently into membrane proteins (JPET 253:993, 1990; JPET 258: 339, 1991). We compared the effects of P-ATP on the second phase of contraction to ATP with those of the 2',3'- dialdehyde (periodate-oxidized) derivatives of ADP (P·ADP), AMP (P-AMP), and adenosine (P-ADO). Upon addition to the bath (10-2 M), P-ATP and P-ADP evoked contraction (P-ATP > P-ADP), while P-AMP and P-ADO did not. After a 5 min incubation and washout, the second phase of response to ATP (10-2 M) was inhibited selectively and irreversibly by P-ATP, P-ADP, and P-AMP. Therefore, inhibition of the second phase was independent of initial agonist activity. P-ADO did not elicit a contraction, and it had no effect on the second phase. These findings suggest that covalent inhibition of ecto-phosphoryl transfer by periodate-oxidized adenosine congeners requires the presence of at least one 5'-phosphate.
The FASEB Journal. Experimental Biology '94, Anaheim, California, April 24-28, 1994